Techniques for User Agent Accessibility Guidelines 1.0
W3C Working Draft, 22 June 2001
- This version:
-
http://www.w3.org/TR/2001/WD-UAAG10-TECHS-20010622/
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- Latest version:
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http://www.w3.org/TR/UAAG10-TECHS/
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http://www.w3.org/TR/2001/WD-UAAG10-TECHS-20010409/
- Editors:
- Ian Jacobs, W3C
Jon Gunderson, University of Illinois at
Urbana-Champaign
Eric Hansen, Educational Testing
Service
- Authors and Contributors:
- See acknowledgements.
Copyright © 1999 - 2001 W3C® (MIT,
INRIA, Keio), All Rights
Reserved. W3C
liability,
trademark, document
use and software
licensing rules apply.
This document provides techniques for satisfying the checkpoints defined in
"Techniques for User Agent Accessibility Guidelines 1.0" [UAAG10]. These
techniques address key aspects of the accessibility of user interfaces, content
rendering, application programming interfaces (APIs), and
languages such as the Hypertext Markup Language (HTML), Cascading Style Sheets
(CSS) and the Synchronized
Multimedia Integration Language (SMIL).
The techniques listed in this document are not required for conformance to
the Guidelines. These techniques are not necessarily the only way of satisfying
the checkpoint, nor are they a definitive set of requirements for satisfying a
checkpoint.
This section describes the status of this document at the time of its
publication. Other documents may supersede this document. The latest status of
this document series is maintained at the W3C.
This is the 22 June 2001 Working Draft of "Techniques for User Agent
Accessibility Guidelines 1.0". It is a draft document and may be updated,
replaced or obsoleted by other documents at any time. It is inappropriate to
use W3C Working Drafts as reference material or to cite them as other than
"work in progress". This is work in progress and does not imply endorsement by,
or the consensus of, either W3C or participants in the User Agent Accessibility
Guidelines Working Group (UAWG).
While Techniques for User Agent Accessibility Guidelines 1.0 strives to be a
stable document (as a W3C Recommendation), the current document is expected to
evolve as technologies change and content developers discover more effective
techniques for designing accessible Web sites and pages.
A list of changes
to this document is available.
Please send comments about this document, including suggestions for
additional techniques, to the public mailing list w3c-wai-ua@w3.org; public archives are
available.
This document is part of a series of accessibility documents published by
the Web Accessibility Initiative (WAI) of the World Wide Web
Consortium (W3C). WAI
Accessibility Guidelines are produced as part of the WAI Technical Activity. The
goals of the User Agent Accessibility
Guidelines Working Group are described in the charter.
A list of current W3C Recommendations and
other technical documents can be found at the W3C Web site.
"Techniques for User Agent Accessibility Guidelines 1.0" and the "User Agent
Accessibility Guidelines 1.0" [UAAG10] are part of a series of
accessibility guidelines published by the Web
Accessibility Initiative (WAI). These documents explain
the responsibilities of user agent developers in making the Web accessibility
to users with disabilities. The series also includes the "Web Content
Accessibility Guidelines 1.0" [WCAG10] (and techniques
[WCAG10-TECHS]), which explain the responsibilities of authors, and
the "Authoring Tool Accessibility Guidelines 1.0" [ATAG10] (and techniques
[ATAG10-TECHS]), which explain the responsibilities of authoring
tool developers.
The Web Accessibility Initiative provides other resources and educational materials
to promote Web accessibility. Resources include information about accessibility
policies, links to translations of WAI materials into languages other than
English, information about specialized user agents and other tools,
accessibility training resources, and more.
In an effort to improve the readability of this document, some information
from User Agent Accessibility Guidelines 1.0 has been copied here:
In an effort to reduce the size of the current document, some information
that is in User Agent Accessibility Guidelines 1.0 has not been copied
here:
- the introduction;
- the descriptions of how the guidelines and checkpoints are structured and
organized;
- the prose of each guideline (i.e., the text after the guideline title and
before the list of checkpoints);
- the conformance section (since one does not conform to the current
document, only to User Agent Accessibility Guidelines 1.0).
The current document includes more (implementation-related) references than the same section inUser Agent
Accessibility Guidelines 1.0, and includes an additional section on resources that should help implementors.
This section lists each checkpoint of "User Agent Accessibility Guidelines
1.0"
[UAAG10] along with some possible techniques for satisfying it. Each
checkpoint definition includes a link to the checkpoint definition in "User
Agent Accessibility Guidelines 1.0". Each checkpoint definition is followed by
one or more of the following:
- Notes and rationale: Additional rationale and explanation
of the checkpoint;
- Who benefits: Which users with disabilities are expected
to benefit from user agents that satisfy the checkpoint;
- Example techniques: Some techniques to illustrate how a
user agent might satisfy the requirements of the checkpoint Screen shots and
other information about deployed user agents have been included as sample
techniques. References to products are not endorsements of those products by
W3C;
- Doing more: Techniques to achieve more than what is
required by the checkpoint;
- Related techniques: Links to other techniques in section
3. The accessibility topics of section 3 generally apply to more than one
checkpoint.
- References: References to other guidelines,
specifications, or resources.
Note: Most of the techniques in this document are designed
for graphical browsers and multimedia players running on desktop computers.
However, some of them also make sense for assistive technologies and other user
agents. In particular, techniques about communication between user agents will
benefit assistive technologies. Refer, for example, to the appendix on loading assistive technologies for access to
the document object model.
Each checkpoint in this document is assigned a priority that indicates its
importance for users with disabilities.
- Priority 1
(P1)
- This checkpoint must be satisfied by user agents,
otherwise one or more groups of users with disabilities will find it impossible
to access the Web. Satisfying this checkpoint is a basic requirement for
enabling some people to access the Web.
- Priority 2
(P2)
- This checkpoint should be satisfied by user agents,
otherwise one or more groups of users with disabilities will find it difficult
to access the Web. Satisfying this checkpoint will remove significant barriers
to Web access for some people.
- Priority 3
(P3)
- This checkpoint may be satisfied by user agents to make it
easier for one or more groups of users with disabilities to access information.
Satisfying this checkpoint will improve access to the Web for some people.
Note: This information about checkpoint priorities is
included for convenience only. For detailed information about conformance to
"User Agent Accessibility Guidelines 1.0" [UAAG10], please refer to that
document.
Checkpoints
1.1 Full keyboard access. (P1)
- Ensure that the user can operate through keyboard input alone any user
agent functionality available through the
user interface.
Both content and user agent.
Checkpoint 1.1
Note: User agents may support at least two types of
keyboard access to functionalities: direct access (where user awareness of a
location "in space" is not required, as is the case with keyboard shortcuts and
navigation of user agent menus) and spatial access (where the user moves the
pointing device "in space" via the keyboard). To satisfy this checkpoint, user
agents are expected to provide a mix of both types of keyboard access. User
agents should allow direct keyboard access where possible, and this may be
redundant with spatial input techniques. Furthermore, the user agent should
satisfy this requirement by offering a combination of keyboard-operable user
interface controls (e.g., keyboard operable print menus and settings) and
direct keyboard operation of user agent functionalities (e.g., a short cut to
print the current page). As examples of functionalities, ensure that the user
can interact with enabled
elements, select content, navigate viewports, configure the user
agent, access documentation, install the user agent, operate controls of the
user interface, etc., all entirely through keyboard input. It is also possible
to claim
conformance to User Agent Accessibility Guidelines 1.0 [UAAG10] for
full support through pointing device input and voice input. See the section on
input modality labels in UAAG 1.0.
Notes and rationale:
- It is up to the user agent developer to decide which functionalities are
best served by direct keyboard access and which are best served by spatial
access through the keyboard (or pointing device). The UAAG 1.0 does not
discourage a pointing device interface, but it does require redundancy through
the keyboard. In most cases, developers can allow operation of the user agent
without relying on motion "through space"; this includes text selection (a text
caret may be used to establish the start and end of the selection), region
selection (allow the user to describe the coordinates or position of the
region, e.g., relative to the viewport), drag-and-drop (allow the user to
designate start and end points and then say "go"), etc.
- For instance, the user must be able to do the following through the
keyboard alone (or pointing device alone or voice alone):
-
Select content and operate on it. For
example, if the user can select rendered text with the mouse and make it the
content of a new link by pushing a button, they also need to be able to do so
through the keyboard and other supported devices. Other operations include cut,
copy, and paste.
- Set the
focus on viewports and on enabled
elements.
- Install, configure, uninstall, and update the user agent software.
- Use the graphical user
interface menus. Some users may wish to user the graphical user
interface even if they cannot use or do not wish to use the pointing
device.
- Fill out forms.
- Access documentation.
- Suppose a user agent does not allow complete operation through the
keyboard alone. It is still possible to claim conformance
for the user agent in conjunction with a special module designed to "fill in
the gap".
Who benefits:
- Users with blindness are most likely to benefit from direct access through
the keyboard, including navigation of user interface controls; this is a
logical navigation, not a spatial navigation.
- Users with physical disabilities are most likely to benefit from a
combination of direct access and spatial access through the keyboard. For some
users with physical disabilities, moving the pointing device through a physical
mouse may be significantly more difficult than moving the pointing device with
arrow keys, for example.
- This checkpoint will also benefit users of many other alternative input
devices (which make use of the keyboard API) and also anyone without a
mouse.
- While keyboard operation is expected to improve access for many users,
operation by keyboard shortcuts alone may reduce accessibility (and usability)
by requiring users to memorize a long list of shortcuts. Developers should
provide mechanisms for contextual access to user agent functionalities
(including keyboard-operable cascading mechanisms, context-sensitive help,
keyboard operable configuration tabs, etc.) as well as direct access to those
functionalities. See also
checkpoint 11.5.
1.2 Activate event handlers.
(P1)
- For the element with content
focus, allow the user to activate
any explicitly associated input device
event handlers through keyboard input alone.
- The user agent is not required to allow activation of event handlers
associated with a given device (e.g., the pointing device) in any order other
than what the device itself allows.
Content only.
Checkpoint 1.2
Note: The requirements for this checkpoint refer to
any explicitly associated input device
event handlers associated with an
element, independent of the input
modalities for which the user agent conforms. For example, suppose that an
element has an explicitly associated handler for pointing device events. Even
when the user agent only conforms for keyboard input (and does not conform for
the pointing device, for example), this checkpoint requires the user agent to
allow the user to activate that handler with the keyboard. This checkpoint is
an important special case of checkpoint 1.1. Please refer to the checkpoints of guideline 9 for more information about
focus requirements.
Notes and rationale:
- For example, users without a pointing device need to be able to activate form
controls and links (including the links in a client-side image
map).
- Events triggered by a particular device generally follow a set pattern, and
often in pairs: start/end, down/up, in/out. One would not expect a "key down"
event for a given key to be followed by another "key down" event without an
intervening "key up" event.
Who benefits:
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques:
- To preserve the expected order of events, provide a dynamically changing
menu of available handlers. For example, an initial menu of handlers might only
allow the user to trigger a "mousedown" event. Once triggered, the menu would
not allow "mousedown" but would allow "mouseup" and "mouseover", etc.
- For example, in HTML 4 [HTML4], input device event handlers
are described in
section 18.2.3. They are:
onclick
, ondblclick
,
onmousedown
, onmouseover
, onmouseout
,
onfocus
, onblur
, onkeypress
,
onkeydown
, and onkeyup
.
- In "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS], focus and activation types are discussed in
section 1.6.1. They are:
DOMFocusIn
, DOMFocusOut
,
and DOMActivate
. These events are specified independent of a
particular input device type.
- In "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS], mouse event types are discussed in
section 1.6.2. They are:
click
, mousedown
,
mouseup
, mouseover
, mousemove
and
mouseout
.
- The DOM Level 2 Event specification does not provide a key event
module.
- Sequential technique: Add each input device event handler to the serial
navigation order (refer to checkpoint
9.3). Alert the user when the user has navigated to an event handler, and
allow activation. For example, an link that also has a onMouseOver and
onMouseOut event handlers defined, might generate three "stops" in the
navigation order: one for the link and two for the event handlers. If this
technique is used, allow configuration so that input device event handlers are
not inserted in the navigation order.
- Query technique: Allow the user to query the element with content focus for
a menu of input device event handlers.
- Descriptive information about handlers can allow assistive technologies to
choose the most important functions for activation. This is possible in the
Java Accessibility API [JAVAAPI], which provides an an
AccessibleAction Java interface. This interface provides a list of actions and
descriptions that enable selective activation. See also checkpoint
6.3.
- Using MSAA
[MSAA] on the Windows platform:
- Retrieve the node in the document object that has current focus.
- Call the
IHTMLDocument4::fireEvent
method on that node.
Related techniques:
- See image map techniques.
References:
- For example,
section 16.5 of the SVG 1.0 Candidate Recommendation [SVG] specifies
processing order for user interface events.
1.3 Provide text messages. (P1)
- Ensure that every message (e.g., prompt, alert, notification, etc.) that is a non-text
element and is part of the user
agent user interface has a text
equivalent.
User agent only. Checkpoint
1.3
Note: For example, if the user is alerted of an event by an
audio cue, a visually-rendered text equivalent in the status bar would satisfy
this checkpoint. Per checkpoint
6.4, a text equivalent for each such message must be available through an
API. See also checkpoint 6.5 for requirements for programmatic alert of
changes to the user interface.
Notes and rationale:
- User agents should use modality-specific messages in the user interface
(e.g., graphical scroll bars, beeps, and flashes) as long as redundant
mechanisms are available or possible. These redundant mechanisms will benefit
all users, not just users with disabilities.
Who benefits:
- Users with blindness, deafness, or who are hard of hearing. Mechanisms that
are redundant to audio will benefit individuals who are deaf, hard of hearing,
or operating the user agent in a noisy or silent environment where the use of
sound is not practical.
Example techniques:
- Render text messages on the status bar of the graphical user interface.
Allow users to query the viewport for this status information (in addition to
having access through graphical rendering).
- Make available information in a manner that allows other software to
present it according to the user's preferences. For instance, if the graphical
user agent uses proportional scroll bars to indicate the position of the
viewport in content, make available this same information in text form. For
instance, this will allow other software to render the proportion of content
viewed as speech or as braille.
Doing more:
- Allow configuration to render or not render status information (e.g., allow
the user to hide the status bar).
Checkpoints
2.1 Render by specification. (P1)
- Render
content according to specification.
- When a rendering requirement of another specification contradicts a
requirement of the current document, the user agent may disregard the rendering
requirement of the other specification and still satisfy this checkpoint.
Content only.
Checkpoint 2.1
Note: Rendering requirements include format-defined
interactions between author preferences and user preferences/capabilities
(e.g., when to render the "alt
"
attribute in HTML [HTML4], the rendering order of
nested OBJECT
elements in HTML, test attributes in SMIL [SMIL], and the
cascade in CSS2
[CSS2]). If a conforming user agent does not render a content type,
it should allow the user to choose a way to handle that content (e.g., by
launching another application, by saving it to disk, etc.). This checkpoint
does not require that all content be available through each viewport. The user agent is not required to
satisfy this checkpoint for all implemented specifications; see the section on
conformance and implementing specifications for more information.
Notes and rationale:
- The right to disregard only applies when the rendering requirement of
another specification contradicts the requirements of the current document; no
exemption is granted if the other specification is consistent with or silent
about a requirement made by the current document.
Who benefits:
- Users with disabilities when specifications include features that promote
accessibility (e.g., scalable graphics benefit users with low vision, style
sheets allow users to override author and user style sheets).
Example techniques:
- Provide access to attribute values (one at a time, not as a group). For
instance, allow the user to select an element and read values for all
attributes set for that element. For many attributes, this type of inspection
should be significantly more usable than a view of the text source.
- When content changes dynamically (e.g., due to embedded scripts or content
refresh), users need to have access to the content before and after the
change.
- Make available information about abbreviation and acronym expansions. For
instance, in HTML, look for abbreviations specified by the ABBR and ACRONYM
elements. The expansion may be given with the "title" attribute (refer to the
Web Content Accessibility Guidelines 1.0 [WCAG10], checkpoint 4.2). To
provide expansion information, user agents may:
- Allow the user to configure that the expansions be used in place of the
abbreviations,
- Provide a list of all abbreviations in the document, with their expansions
(a generated glossary of sorts)
- Generate a link from an abbreviation to its expansion.
- Allow the user to query the expansion of a selected or input
abbreviation.
- If an acronym has no expansion in one location, look for another occurrence
in content that does. User agents may also look for possible expansions (e.g.,
in parentheses) in surrounding context, though that is a less reliable
technique.
Related techniques:
- See the sections on access to content, link techniques, table
techniques, frame techniques, and form techniques.
Doing more:
- If the requirements of the current document contradict the rendering
requirements of another specification, the user agent may offer a configuration
to allow conformance to one or the other specification.
References:
- Sections 10.4 ("Client Error 4xx") and 10.5 ("Server Error 5xx") of the
HTTP/1.1 specification [RFC2616] state that user agents
should have the following behavior in case of these error conditions:
Except when responding to a HEAD request, the server SHOULD include an
entity containing an explanation of the error situation, and whether it is a
temporary or permanent condition. These status codes are applicable to any
request method. User agents SHOULD display any included entity to the user.
2.2 Provide text view. (P1)
- For text formats, provide a view of the text source. For the purposes of this document,
text formats are defined to be:
- all media objects given an Internet media type of "text" (e.g., text/plain,
text/HTML, or text/*), and
- all SGML and XML applications, regardless of Internet media type (e.g.,
HTML 4.01, XHTML 1.1, SMIL, SVG, etc.).
Content only.
Checkpoint 2.2
Note: Refer to [RFC2046], section 4.1 for
information about the "text" Internet media type. A user agent would also
satisfy this checkpoint by providing a source view for any text format, not
just implemented text formats. The user agent is not required to satisfy this
checkpoint for all implemented specifications; see the section on
conformance and implementing specifications for more information.
Notes and rationale:
- In general, user agent developers should not rely on a "source view" to
convey information to users, most of whom are not familiar with markup
languages. A source view is still important as a "last resort" to some users as
content might not otherwise be accessible at all.
Who benefits:
- Users with blindness, low vision, deafness, hard of hearing, and any user
who requires the text source to understand the content.
Example techniques:
- Make the text view useful. For instance, enable links (i.e.,
URIs), allowing searching and other navigation within the view.
- A source view is an easily-implementable view that will help users inspect
some types of content, such as style sheet fragments or scripts. This does not
mean, however, that a source view of style sheets is the best user
interface for reading or changing style sheets.
Doing more:
- Provide a source view for any text format, not just implemented text
formats.
2.3
Render conditional content. (P1)
- Allow
configuration to provide access to each piece of unrendered
conditional content "C".
- The configuration may be a switch that, for all content, turns on or off
the access mechanisms described in the following statements.
- When a specification does not explain how to provide access to this
content, do so as follows:
- If C is a summary, title, alternative, description, or expansion of another
piece of content D, provide access through at least one of the following
mechanisms:
- (1a) render C in place of D;
- (2a) render C in addition to D;
- (3a) provide access to C by querying D. In this case, the user agent must
also alert the user, on a per-element basis, to the existence of "C" (so that
the user knows to query D);
- (4a) allow the user to follow a link to C from the context of D.
- Otherwise, provide access to C through at least one of the following
mechanisms:
- (1b) render a
placeholder for C, and allow the user to view the original
author-supplied content associated with each placeholder;
- (2b) provide access to C by query (e.g., allow the user to query an element
for its
attributes). In this case, the user agent must also alert the user,
on a per-element basis, to the existence of "C";
- (3b) allow the user to follow a link in context to C.
Content only.
Checkpoint 2.3
Note: To satisfy this checkpoint, the user agent may
provide access on an per-element basis (e.g., by allowing the user to query
individual elements) or for all elements (e.g., by offering a configuration to
render conditional content all the time). For instance, an HTML user agent
might allow users to query each element for access to conditional content
supplied for the "alt
", "title
", and
"longdesc
" attributes. Or, the user agent might allow
configuration so that the value of the "alt
" attribute is rendered
in place of all IMG
elements (while other conditional content
might be made available through another mechanism). See checkpoint 2.10 for
additional placeholder requirements.
Notes and rationale:
- There may be more than one piece of conditional content associated with
another piece of content (e.g., multiple captions tracks associated with the
visual track of a presentation).
- Please note that the alert requirement of this checkpoint is per-element. A
single resource-level alert (e.g., "there is conditional content somewhere
here") does not satisfy the checkpoint, but may be part of a solution for
satisfying this checkpoint. For example, the user agent might indicate the
presence of conditional content "somewhere" with menu in the toolbar. The menu
items could provide both per-element alert and access to the content (e.g., by
opening a viewport with the conditional content rendered).
Who benefits:
- Any user for whom the author has provided conditional content for
accessibility purposes. This includes: text equivalents for users with
blindness or low vision, or users who are deaf-blind, and captions, for users
who with deafness or who are hard of hearing.
Example techniques:
- Allow users to choose more than one piece of
conditional content at a given time. For instance,users with low
vision may want to view images (even imperfectly) but require a text equivalent for the image; the text may be rendered with a large font or as
speech.
- In HTML 4 [HTML4], conditional content
mechanisms include the following:
- Allow the user to
configure how the user agent renders a long description (e.g., "longdesc"
in HTML 4 [HTML4]). Some possibilities
include:
- Render the long description in a separate view.
- Render the long description in place of the associated element.
- Do not render the long description, but allow the user to query whether an
element has an associated long description (e.g., with a context-sensitive
menu) and provide access to it.
- Use an icon (with a text
equivalent) to indicate the presence of a long description.
- Use an audio cue to indicate the presence of a long description when the
user navigates to the element.
- For an object (e.g., an image) with an author-specified geometry that the
user agent does not render, allow the user to configure how the conditional
content should be rendered. For example, within the specified geometry, by
ignoring the specified geometry altogether, etc.
- For multimedia presentations with several alternative tracks, ensure access
to all tracks and allow the user to select individual tracks. The QuickTime
player
[QUICKTIME] allows users to turn on and off any number of tracks
separately. For example, construct a list of all available tracks from short
descriptions provided by the author (e.g., through the "title" attribute).
- For multimedia presentations with several alternative tracks, allow users
to choose tracks based on natural
language preferences. SMIL 1.0 [SMIL] allows users to specify captions in different natural languages. By
setting language preferences in the SMIL player (e.g., the G2 player [G2]), users may access
captions (or audio) in different languages. Allow users to specify different
languages for different content types (e.g., English audio and Spanish
captions).
- If a multimedia presentation has several
captions (or subtitles) available, allow the user to choose from
among them. Captions might differ in level of detail, reading levels, natural
language, etc. Multilingual audiences may wish to have captions in
different natural
languages on the screen at the same time. Users may wish to use both
captions and auditory descriptions concurrently as well.
- Make apparent through the user
agent user interface which audio
tracks are meant to be played separately.
Related techniques:
- See the section on access to content.
Doing more:
- Make information available with different levels of detail. For example,
for a voice
browser, offer two options for HTML
IMG
elements:
- Speak only "alt" text by default, but allow the user to hear "longdesc"
text on an image by image basis.
- Speak "alt" text and "longdesc" for all images.
- Allow the user to configure different natural language preferences for different
types of
conditional content (e.g., captions and auditory descriptions).
Users with disabilities may need to choose the language they are most familiar
with in order to understand a presentation for which supplementary tracks are
not all available in all desired languages. In addition, some users may prefer
to hear the program audio in its original language while reading captions in
another, fulfilling the function of subtitles or to improve foreign language
comprehension. In classrooms, teachers may wish to configure the language of
various multimedia elements to achieve specific educational goals.
2.4 Allow time-independent interaction.
(P1)
- For
content where user input is only possible
within a finite time interval controlled by the user agent, allow configuration to make the time interval
"infinite". Do this by pausing automatically at the end of each time interval
where user input is possible, and resuming automatically after the user has
explicitly completed input.
- In this configuration, alert the user when the session has been paused and
which enabled
elements are time-sensitive.
- When the user pauses a real-time presentation, the user agent may discard
packets that continue to arrive during the pause.
Content only.
Checkpoint 2.4
Note: In this configuration, the user agent may have to
pause the presentation more than once if there is more than one opportunity for
time-sensitive input. Per
checkpoint 2.6, when the user pauses one piece of a synchronized
presentation, the user agent should pause all of the pieces (whether they are
rendered in the same or different viewports). In SMIL 1.0 [SMIL], for example,
the "begin
", "end
", and "dur
" attributes synchronize presentation components.
The user may explicitly complete input in many different ways (e.g., by
following a link that replaces the current time-sensitive resource with a
different resource). This checkpoint does not apply when
the user agent cannot recognize
the time interval in the presentation format, or when the user agent cannot
control the timing (e.g., because it is controlled by the server).
See also checkpoint 3.5, which involves client-driven content
refresh.
Notes and rationale:
- The requirement to pause at the end (rather than at the beginning)
of a time-interval is to allow the user to review content that may change
during the elapse of this time.
- This checkpoint requires the user agent to pause a presentation
automatically, whereas the pause requirement of checkpoint 4.5 is
manual.
- The configuration option is important because automatic pause may lead to
information loss for types of content (e.g., highly interactive real-time
presentations).
- When different streams of time-sensitive content are not synchronized (and
rendered in the same or different viewports), the user agent is not required to
pause the pieces all at once. The assumption is that both streams of content
will be available at another time.
Who benefits:
- Some users with a physical disability who may not have the time to interact
with the content. Also, users who may be accessing the content serially (e.g,.
users with blindness or some users with a physical disability) and require more
time to reach the timed content
Example techniques:
- Some HTML user agents recognize time intervals specified through the
META
element, although this usage is not defined in HTML 4 [HTML4].
- Render time-dependent links as a static list that occupies the same screen
real estate; authors may create such documents in SMIL 1.0 [SMIL]. Include
temporal context in the list of links. For example, provide the time at which
the link appeared along with a way to easily jump to that portion of the
presentation.
- For a presentation that is not "live", allow the user to choose from a menu
of available time-sensitive links (essentially making them
time-independent).
Doing more:
- The checkpoint requires that the user agent make the time interval
infinite, but one consequence of this is that the user needs to confirm
manually the end of input. The user agent may provide additional configurations
to lengthen time intervals so that manual confirmation at the end of input is
not required. For instance, the user agent might include a configuration to
allow the user three to five times the author's specified time interval for
input. Or, the user agent might include a configuration to add additional time
to each time interval (e.g., 10 extra seconds).
- Allow users to view a list of all media elements or links of the
presentations sorted by start or end time or alphabetically.
- Alert the user whenever pausing the user agent may lead to packet
loss.
References:
- Refer to section
4.2.4 of SMIL 1.0
[SMIL] for information about the SMIL time model.
2.5 Make captions, transcripts available.
(P1)
- Allow
configuration or control so
that text
transcripts,
collated text transcripts, captions,
and auditory
descriptions are rendered at the same time as the associated audio tracks and
visual tracks.
Content only.
Checkpoint 2.5
Note: This checkpoint is an important special case of checkpoint 2.1.
Notes and rationale:
- Users may wish to a read transcript at the same time as a related visual or
audio track and pause the visual or audio track while reading; see checkpoint 4.5.
Who benefits:
- Users with blindness or low vision (auditory descriptions and text
captions, etc.) and users with deafness or who are hard of hearing.
Example techniques:
- Allow users to turn on and off auditory descriptions and captions.
- For the purpose of applying this clause, SMIL 1.0 [SMIL] user agents should recognize
as captions any media object whose reference from SMIL is guarded by the
'
system-captions
' test attribute.
- SMIL user agents should allow users to configure whether they want to view
captions, and this user interface switch should be bound to the
'
system-captions
' test attribute. Users should be able to indicate
a preference for receiving available auditory descriptions, but SMIL 1.0
[SMIL] does not
include a mechanism analogous to 'system-captions' for auditory descriptions,
though
[SMIL20] is expected to.
- Another SMIL 1.0 test attribute, '
system-overdub-or-captions
',
allows users to choose between subtitles and overdubs in multilingual
presentations. User agents should not interpret a value of
'caption
' for this test attribute as meaning that the user prefers
accessibility captions; that is the purpose of the
'system-captions
' test attribute. When subtitles and accessibility
captions are both available, users who are deaf may prefer to view captions, as
they generally contain information not in subtitles: information on music,
sound effects, who is speaking, etc.
- User agents that play QuickTime movies should allow the user to turn on and
off the different tracks embedded in the movie. Authors may use these
alternative tracks to provide content for accessibility purposes. The Apple
QuickTime player provides this feature through the menu item "Enable
Tracks."
- User agents that play Microsoft Windows Media Object presentations should
provide support for Synchronized Accessible Media Interchange (SAMI [SAMI]), a protocol
for creating and displaying captions) and should allow users to configure how
captions are viewed. In addition, user agents that play Microsoft Windows Media
Object presentations should allow users to turn on and off other
conditional content, including auditory description and alternative
visual tracks.
References:
- User agents that implement SMIL 1.0 [SMIL] should implement the
"Accessibility Features of SMIL" [SMIL-ACCESS].
2.6 Respect synchronization cues.
(P1)
- Respect synchronization cues during rendering.
Content only.
Checkpoint 2.6
Note: This checkpoint is an important special case of checkpoint 2.1.
Notes and rationale:
- The term "synchronization cues" refers to pieces of information that may
affect synchronization, such as the size and expected duration of tracks and
their segments, the type of element and how much those elements can be sped up
or slowed down (both from technological and intelligibility standpoints).
- Captions and auditory
descriptions may not make sense unless rendered synchronously with
related video or audio content. For instance, if someone with a hearing
disability is watching a video presentation and reading associated captions,
the captions should be
synchronized with the audio so that the individual can use any
residual hearing. For auditory descriptions, it is crucial that an audio track and an auditory description track
be synchronized to avoid having them both play at once, which would reduce the
clarity of the presentation.
Who benefits:
- Users with deafness or who are hard of hearing (e.g., for auditory
descriptions and audio tracks), and some users with a cognitive
disability.
Example techniques:
- For synchronization in SMIL 2.0 [SMIL20], refer to section
10, the timing and synchronization module.
- The idea of "sensible time-coordination" of components in the definition of
synchronize centers on the idea of
simultaneity of presentation, but also encompasses strategies for handling
deviations from simultaneity resulting from a variety of causes. Consider how
deviations might be handled for captions
for a multimedia presentation such as a movie clip. Captions consist of a text
equivalent of the audio track that is synchronized with the
visual track. Typically, a segment of the
captions appears visually near the video for several seconds while the person
reads the text. As the visual track continues, a new segment of the captions is
presented. However, a problem arises if the captions are longer than can fit in
the display space. This can be particularly difficult if due to a visual
disability, the font size has been enlarged, thus reducing the amount of
rendered caption text that can be presented. The user agent needs to respond
sensibly to such problems, for example by ensuring that the user has the
opportunity to navigate (e.g., scroll down or page down) through the caption
segment before proceeding with the visual presentation and presenting the next
segment.
- Developers of user agents need to determine how they will handle other
synchronization challenges, such as:
- Under what circumstances will the presentation automatically pause? Some
circumstances where this might occur include:
- the segment of rendered caption text is more than can fit on the visual
display
- the user wishes more time to read captions or the collated text
transcript
- the auditory description is of longer duration than the natural pause in
the audio.
- Once the presentation has paused, then under what circumstances will it
resume (e.g., only when the user signals it to resume, or based on a predefined
pause length)?
- If the user agent allows the user to jump to a location in a presentation
by activating a link, then how will related tracks behave? Will they jump as
well? Will the user be able to return to a previous location or undo the
action?
- Developers of user agents need to anticipate many of the challenges that
may arise in synchronization of diverse tracks.
2.7 Repair missing content. (P2)
- Allow
configuration to generate repair
text when the user agent
recognizes that the author has failed to provide
conditional content that was required by the format
specification.
- The user agent may satisfy this checkpoint by basing the repair text on any
of the following available sources of information: URI reference, content type,
or element type.
Content only. Checkpoint
2.7
Note: Some markup languages (such as HTML 4 [HTML4] and SMIL
1.0 [SMIL]
require the author to provide conditional content for some elements (e.g., the
"alt
" attribute
on the IMG
element). Repair text based on URI reference, content
type, or element type is sufficient to satisfy the checkpoint, but may not
result in the most effective repair. Information that may be recognized as relevant to repair might not be
"near" the missing conditional content in the document object. For instance, instead of
generating repair text on a simple URI reference, the user agent might look for
helpful information near a different instance of the URI reference in the same
document object, or might retrieve useful information (e.g., a title) from the
resource designed by the URI reference.
Notes and rationale:
- Some examples of missing conditional content that is required by
specification:
- in HTML 4
[HTML4], "
alt
" is required for the IMG
and
AREA
elements (for validation). In SMIL 1.0 [SMIL], on the other
hand, "alt
" is not required on media objects.
- whatever the format, text equivalents for non-text content are required by
the Web Content Accessibility Guidelines 1.0 [WCAG10].
- Conditional content may come from markup, inside images (e.g., refer to
"Describing and retrieving photos using RDF and HTTP"
[PHOTO-RDF]), etc.
Who benefits:
- Users with blindness or low vision.
Example techniques:
- When HTTP is used, HTTP headers provide information about the URI of the
Web resource ("Content-Location") and its
type ("Content-Type"). Refer to the HTTP/1.1 specification [RFC2616],
sections 14.14 and 14.17, respectively. Refer to "Uniform Resource Identifiers
(URI): Generic Syntax" ([RFC2396], section 4) for
information about URI references, as well as the HTTP/1.1 specification
[RFC2616],
section 3.2.1.
Related techniques:
- See content repair techniques, and cell header repair strategies.
Doing more:
- When configured to generate text, also inform the user (e.g., in the
generated text itself) that this content was not provided by the author as a
text equivalent.
References:
- The "Altifier Tool" [ALTIFIER] illustrates smart
techniques for generating text
equivalents (for images, etc.) when the author has not specified
any.
2.8 No repair text.
(P3)
- Allow at least two
configurations for when the user agent
recognizes that
conditional content required by the format specification is present
but
empty:
Content only. Checkpoint
2.8
Note: In some authoring scenarios, empty content (e.g., a
string of zero characters) may make an appropriate text equivalent, such as when non-text
content has no other function than pure decoration, or when an image
is part of a "mosaic" of several images and doesn't make sense out of the
mosaic. Please refer to the Web Content Accessibility Guidelines 1.0 [WCAG10] for
more information about text equivalents.
Notes and rationale:
- User agents should render nothing in this case because the author may
specify an empty
text equivalent for content that has no function in the page other than as
decoration.
Who benefits:
- Users with blindness or low vision.
Example techniques:
- The user agent should not render generic labels such as "[INLINE]" or
"[GRAPHIC]" in the face of empty
conditional content (unless configured to do so).
- If no captioning information is available and captioning is turned on,
render "no captioning information available" in the captioning region of the
viewport (unless configured not to generate repair content).
Doing more:
- Labels (e.g., "[INLINE]" or "[GRAPHIC]") may be useful in some situations,
so the user agent may allow configuration to render "No author text" (or
similar) instead of empty conditional content.
2.9 Render conditional
content automatically. (P3)
- Allow
configuration to render all conditional content automatically. The user
agent is not required to render all conditional content at the same time in a
single viewport.
- Provide access to this content according to format specifications or where
unspecified, by applying one of the following techniques described in checkpoint 2.3: 1a, 2a, or
1b.
Content only.
Checkpoint 2.9
Note: The user agent satisfies this checkpoint if it
satisfies checkpoint 2.3
by applying techniques 1a, 2a, or 1b. For instance, an HTML user agent might
allow configuration so that the value of the "alt
" attribute is rendered in place of all
IMG
elements (while other conditional content might be made available
through another mechanism). The user agent may offer multiple configurations
(e.g., a first configuration to render one type of conditional content
automatically, a second to render another type, etc.).
Who benefits:
- Any user who may have difficulties with navigation and manual access to
content, including some users with a physical disability and users with
blindness or low vision.
Example techniques:
- Provide a "conditional content view", where all content that is not
rendered by default is rendered in place of associated content. For example,
Amaya
[AMAYA] offers a "Show alternate" view that accomplishes this. Note,
however, cases where an element has more than one piece of associated
conditional content (e.g., render them all as a list, or as a list of links,
etc.). For long conditional content, instead of rendering in place, link to the
content.
2.10
Toggle placeholders. (P3)
- Once the user has viewed the original author-supplied content associated
with a
placeholder, allow the user to turn off the rendering of the
author-supplied content.
Content only.
Checkpoint 2.10
Note: For example, if the user agent substitutes the
author-supplied content for the placeholder in context, allow the user to
"toggle" between placeholder and the associated content. Or, if the user agent
renders the author-supplied content in a separate viewport, allow the user to
close that viewport. Note: See checkpoint 2.3 for
placeholder requirements.
Who benefits:
- Some users with a cognitive disability may find it difficult to access
content once too many images (for example) have been rendered one by one.
Example techniques:
- Allow the user to designate a placeholder and request to view the
associated content in a separate viewport (e.g., through the context menu),
leaving the placeholder in context. Per checkpoint 5.3, users are able to close the new
viewport.
2.11 Alert unsupported language.
(P3)
- Allow
configuration not to render content in unsupported natural
languages (including scripts,
i.e., writing systems). Indicate to the user in context that author-supplied
content has not been rendered.
Content only.
Checkpoint 2.11
Note: For example, use a text substitute or accessible
graphical icon to indicate that content in a particular language has not been
rendered. This checkpoint does not require the user agent to allow different
configurations for different natural languages.
Notes and rationale:
- A script is a means of supporting the visual rendering of content in a
particular natural language. So, for user agents that render content visually,
a user agent might not recognize "the Cyrillic script", which would mean that
it would not support the visual rendering of Russian, Ukrainian, and other
languages that employ Cyrillic when written.
- Rendering content in an unsupported language (e.g., as "garbage"
characters) may confuse all users. However, this checkpoint is designed
primarily to benefit users who access content serially as it allows them to
skip portions of content that would be unusable as rendered.
- There may be cases when a conforming user agent supports a natural language
but a speech synthesizer does not, or vice versa.
Who benefits:
- Users who access content serially, including users with blindness and some
users with a physical disability.
Example techniques:
- For instance, a user agent that doesn't support Korean (e.g., doesn't have
the appropriate fonts or voice set) should allow configuration to announce the
language change with the message "Unsupported language – unable to
render" (e.g., when the language itself is not recognized) or "Korean not
supported – unable to render" (e.g., when the language is recognized by
the user agent doesn't have resources to render it). The user should also be
able to choose no alert of language changes. Rendering could involve speaking
in the designated natural language in the case of a voice browser or screen
reader. If the natural language is not supported, the language change alert
could be spoken in the default language by a screen reader or
voice browser.
- A user agent may not be able to render all characters in a document
meaningfully, for instance, because the user agent lacks a suitable font, a
character has a value that may not be expressed in the user agent's internal
character encoding, etc. In this case,
section 5.4 of HTML 4 [HTML4] recommends the following for
undisplayable characters:
- Adopt a clearly visible (or audible), but unobtrusive mechanism to alert
the user of missing resources.
- If missing characters are presented using their numeric representation, use
the hexadecimal (not decimal) form since this is the form used in character set
standards.
- When HTTP is used, HTTP headers provide information about content encoding
("Content-Encoding") and content language ("Content-Language"). Refer to the
HTTP/1.1 specification [RFC2616], sections 14.11 and
14.12, respectively.
- CSS2's attribute selector may be used with the HTML "lang" or XML
"xml:lang" attributes to control rendering based on
recognized natural language information. Refer also to the ':lang'
pseudo-class ([CSS2], section 5.11.4).
Related techniques:
- See techniques for generated content,
which may be used to insert text to
indicate a language change.
- See content repair techniques and accessibility and internationalization
techniques.
- See techniques for synthesized
speech.
References:
- For information on language codes, refer to "Codes for the representation
of names of languages" [ISO639].
- Refer to "Character Model for the World Wide Web" [CHARMOD]. It
contains basic definitions and models, specifications to be used by other
specifications or directly by implementations, and explanatory material. In
particular, this document addresses early uniform normalization, string
identity matching, string indexing, and conventions for URIs.
In addition to the techniques below, refer also to the section on user control of style.
Checkpoints
3.1 Toggle background images.
(P1)
- Allow
configuration not to render background images.
- In this configuration, the user agent is not required to retrieve
background images from the Web.
- This checkpoint only requires control of background images for "two-layered
renderings", i.e., one rendered background image with all other content
rendered "above it".
Content only.
Checkpoint 3.1
Note: See checkpoint 2.3 for information about how to provide access
to unrendered background images. When background images are not rendered, user
agents should render a solid background color instead (see checkpoint 4.3).
Notes and rationale:
- This checkpoint does not address issues of multi-layered renderings and
does not require the user agent to change background rendering for multi-layer
renderings (refer, for example, to the 'z-index' property in Cascading Style
Sheets, level 2 ([CSS2], section 9.9.1).
Who benefits:
- Some users with a cognitive disability or color deficiencies who may find
it difficult or impossible to read superimposed text or understand other
superimposed content.
Example techniques:
- If background image are turned off, make available to the user associated
conditional content.
- In CSS, background images may be turned on/off with the
'background' and 'background-image' properties ([CSS2], section 14.2.1).
Doing more:
- Allow control of image depth in multi-layer presentations.
3.2
Toggle audio, video, animated images. (P1)
- Allow
configuration not to render audio, video, or animated images except
on explicit
user request.
- The user agent may satisfy this checkpoint by making video and animated
images
invisible and audio
silent, but this technique is not recommended.
Content only.
Checkpoint 3.2
Note: See checkpoint 2.3 for information about how to provide access
to unrendered audio, video, and animated images. This checkpoint requires
configuration for content rendered without any user interaction (including
content rendered on load or as the result of a script), as well as content
rendered as the result of user interaction (e.g., when the user activates a
link). When configured not to render content except on explicit user request,
the user agent is not required to retrieve the audio, video, or animated image
from the Web until requested by the user. See also checkpoint 4.5, checkpoint 4.9, and checkpoint 4.10.
Who benefits:
- Some users with a cognitive disability, for whom an excess of visual
information (and in particular animated information) might it impossible to
understand parts of content. Also, audio rendered automatically on load may
interfere with speech synthesizers.
Example techniques:
- For user agents that hand off content to different rendering engines, the
configuration should cause the content not to be handed off, and instead a
placeholder rendered.
- The "silent" or "invisible" solution for satisfying this checkpoint (e.g.,
by implementing the
'visibility' property defined in section 11.2 of CSS 2 [CSS2]). is not
recommended. This solution means that the content is processed, though not
rendered, and processing may cause undesirable side effects such as firing
events. Or, processing may interfere with the processing of other content
(e.g., silent audio may interfere with other sources of sound such as the
output of a speech synthesizer). This technique should be deployed with
caution.
- As a placeholder for an animated image, render a motionless image built
from the first frame of the animated image.
3.3
Toggle animated/blinking text. (P1)
- Allow
configuration to render animated or blinking text as motionless,
unblinking text.
- In this configuration, the user must still have access to the same text
content, but the user agent may render it in a separate viewport (e.g., for
large amounts of streaming text).
- The user agent also satisfies this checkpoint by always rendering animated
or blinking text as motionless, unblinking text.
Content only.
Checkpoint 3.3
Note: Animation (a rendering effect) is different from
streaming (a delivery mechanism). Streaming content may be rendered as an
animation (e.g., an animated stock ticker) or as static text (e.g., movie
subtitles, which are rendered for a limited time, but do not give the
impression of movement). Blinking text is text whose visual rendering
alternates between visible and invisible, any any rate of change. See also checkpoint 3.5. apply for
blinking and animation
effects that are caused by mechanisms that the user agent cannot
recognize.
Notes and rationale:
- The definition of blinking text is based on the CSS2 definition of the
'blink' value; refer to [CSS2], section 16.3.1.
Who benefits:
- Flashing content may trigger seizures in people with photosensitive
epilepsy, or may make a Web page too distracting to be usable by someone with a
cognitive disability. Blinking text can affect screen reader users, since
screen readers (in conjunction with speech synthesizers or braille displays)
may re-render the text every time it blinks.
- Configuration is preferred as some users may benefit from blinking effects
(e.g., users who are deaf or hard of hearing). However, the priority of this
checkpoint was assigned on the basis of requirements unrelated to this
benefit.
Example techniques:
- The user agent may render the motionless text in a number of ways. Inline
is preferred, but for extremely long text, it may be better to render the text
in another viewport, easily reachable from the user's browsing context.
- Allow the user to turn off animated or blinking text through the user
agent user interface (e.g., by pressing the Escape key to
stop animations).
- Some sources of blinking and moving text are:
- The BLINK element in HTML. Note: The BLINK element is not
defined by a W3C specification.
- The MARQUEE element in HTML. Note: The MARQUEE element is
not defined by a W3C specification.
- The 'blink' value of the
'text-decoration' property in CSS ([CSS2], section 16.3.1).
- In JavaScript, to control the start and speed of scrolling for a
MARQUEE
element:
document.all.myBanner.start();
document.all.myBanner.scrollDelay = 100
3.4 Toggle scripts. (P1)
- Allow
configuration not to execute any executable
content (e.g., scripts and
applets).
- In this configuration, provide an option to alert the user when executable
content is available (but has not been executed).
- The user agent is only required to alert the user to the presence of more
than zero scripts or applets (i.e., per-element alerts are not required).
Content only.
Checkpoint 3.4
Note: This checkpoint does not refer to plug-ins and other programs that are not part
of content. Scripts and applets may provide very
useful functionality, not all of which causes accessibility problems.
Developers should not consider that the user's ability to turn off scripts is
an effective way to improve content accessibility; turning off scripts means
losing the benefits they offer. Instead, developers should provide users with
finer control over user agent or content behavior known to raise accessibility
barriers. The user should only have to turn off scripts as a last resort.
Notes and rationale:
- Executable content includes scripts, applets,
ActiveX controls, etc. This checkpoint does not apply to
plug-ins; they are not part of
content.
- Executable content includes those that run "on load" (e.g., when a document
loads into a viewport) and when other events occur (e.g., user interface
events).
- The alert that scripts are available but not executed is important, for
instance, for helping users understand why some poorly authored pages without
script alternatives produce no content when scripts are turned off.
- Where possible, authors should encode knowledge in declarative formats
rather than in scripts. Knowledge and behaviors embedded in scripts is
difficult to extract, which means that user agents are less likely to be able
to offer control by the user over the script's effect.
Who benefits:
- Control of executable content is particularly important as it can cause the
screen to flicker, since people with photosensitive epilepsy can have seizures
triggered by flickering or flashing, particularly in the 4 to 59 flashes per
second (Hertz) range. Peak sensitivity to flickering or flashing occurs at 20
Hertz.
Example techniques:
- Do not make available the switch to turn scripts off only in the "Security"
part of the user interface as people may not think to look there. For instance,
include a "Scripts" entry in the index that allows people to find the switch
more easily.
Related techniques:
- See the section on script techniques.
Doing more:
- While this checkpoint only requires an on/off configuration switch, user
agents should allow finer control over executable content. For instance, in
addition to the switch, allow users to turn off just input device event
handlers, or to turn on and off scripts in a given scripting language
only.
3.5 Toggle content refresh. (P1)
- Allow
configuration so that the user agent only refreshes content on explicit user request.
- In this configuration, alert the user of the refresh rate specified in
content, and allow the user to request fresh content manually (e.g., by
following a link or confirming a prompt).
- When the user chooses not to refresh content, the user agent may ignore
that content; buffering is not required.
- This checkpoint only applies when the user agent (not the server)
automatically initiates the request for fresh content.
Content only.
Checkpoint 3.5
Note: For example, allow configuration to prompt the user
to confirm content refresh, at the rate specified by the author.
Notes and rationale:
- Some HTML authors create a refresh effect by using a
META element with http-equiv="refresh" and the refresh rate specified in
seconds by the "content" attribute.
Who benefits:
- Automatically changing content can disorient some users with a cognitive
disability, users with blindness or low vision, and most users.
Example techniques:
- Alert the user that suppressing refresh may lead to loss of information
(i.e., packet loss).
Doing more:
- Allow users to specify their own refresh rate.
- Allow configuration for at least one very slow refresh rate (e.g., every 10
minutes).
- Retrieve new content without displaying it automatically. Allow the user to
view the differences (e.g., by highlighting or filtering) between the currently
rendered content and the new content (including no differences).
3.6 Toggle redirects. (P2)
- Allow
configuration so that a "client-side redirect" (i.e., one initiated
by the user agent, not the server) only changes
content on explicit
user request.
- Allow the user to access the new content on demand (e.g., by following a
link or confirming a prompt).
- The user agent is not required to provide these functionalities for
client-side redirects specified to occur instantaneously (i.e., after no
delay).
Content only.
Checkpoint 3.6
Notes and rationale:
- Some HTML authors create client-side redirects using a
META element with http-equiv="refresh". Authors (and Web masters) should use
HTTP's redirect mechanisms instead.
- This checkpoint is a Priority 2 checkpoint in part because the author's
redirect implies that users aren't expected to use the content prior to the
redirect.
Who benefits:
- Automatically changing content can disorient some users with a cognitive
disability, users with blindness or low vision, and most users.
Example techniques:
- Provide a configuration so that when the user navigates "back" through the
user agent history to a page with a client-side redirect, the user agent does
not re-execute the client-side redirect.
Doing more:
- Allow configuration to allow access on demand to new content even when the
client-side redirect has been specified by the author to be instantaneous.
References:
- For Web content authors: refer to the HTTP/1.1 specification [RFC2616] for
information about using server-side redirect mechanisms (instead of client-side
redirects).
3.7 Toggle images. (P2)
- Allow
configuration not to render images.
- The user agent may satisfy this checkpoint by making images
invisible, but this technique is not recommended.
Content only.
Checkpoint 3.7
Note: See checkpoint 2.3 for information about how to provide access
to unrendered images.
Notes and rationale:
- This priority of
checkpoint 3.2 is higher than the priority of this checkpoint because an
excess of moving visual information is likely to be more distracting to some
users than an excess of still visual information.
Who benefits:
- Some users with a cognitive disability, for whom an excess of visual
information might it difficult to understand parts of content.
Related techniques:
- See techniques for checkpoint 3.1.
In addition to the techniques below, refer also to the section on user control of style.
Checkpoints for visually rendered text
4.1
Configure text size. (P1)
- Allow global
configuration and control
over the reference size of visually rendered
text, with an option to override
reference sizes specified by the author or user agent defaults.
- Allow the user to choose from among the full range of font sizes supported
by the
operating environment.
Content only.
Checkpoint 4.1
Note: The reference size of rendered text corresponds to
the default value of the CSS2 'font-size' property, which is 'medium' (refer to
CSS2
[CSS2], section 15.2.4). For example, in HTML, this might be
paragraph text. The default reference size of rendered text may vary among user
agents. User agents may offer different mechanisms to allow control of the size
of rendered text (e.g., font size control, zoom, magnification, etc.). Refer,
for example to the Scalable Vector Graphics specification [SVG] for information
about scalable rendering.
Notes and rationale:
- For example, allow the user to configure the user agent to apply the same
font family across Web resources, so that all
text is displayed by default using that font family. Or, allow the
user to control the text size dynamically for a given element, e.g., by
navigating to the element and zooming in on it.
- The choice of optimal techniques depends in part on which markup language
is being used. For instance, HTML user agents may allow the user to change the
font size of a particular piece of text (e.g., by
using CSS user style sheets) independent of other content (e.g., images). Since
the user agent can reflow the text after resizing the font, the rendered text
will become more legible without, for example, distorting bitmap images. On the
other hand, some languages, such as SVG, do not allow text reflow, which means
that changes to font size may cause rendered text to overlap with other
content, reducing accessibility. SVG is designed to scale, making a zoom
functionality the more natural technique for SVG user agents satisfying this
checkpoint.
- The primary intention of this checkpoint is to allow users with low vision
to increase the size of text. Full configurability includes the choice of
(very) small text sizes that may be available, though this is not considered by
the User Agent Accessibility Guidelines Working Group to be part of the
priority 1 requirement. This checkpoint does not include a "lower bound" (above
which text sizes would be required) because of how users' needs may vary across
writing systems and hardware.
Who benefits:
- Users with low vision benefit from the ability to increase the text size.
Note that some users may also benefit from the ability to choose small font
sizes (e.g., users of screen readers who wish to have more content per screen
so they have to scroll less frequently).
Example techniques:
- Inherit text size information from user preferences specified for the
operating environment.
- Use
operating environment magnification features.
- When scaling text, maintain size relationships among text of different
sizes.
- Implement the
'font-size' property in CSS ([CSS2], section 15.2.4).
Doing more:
- Allow the user to configure the text size on an element level (i.e., more
precisely than globally). User style sheets allow such detailed
configurations.
- Allow the user to configure the text size differently for different scripts (i.e., writing systems).
4.2 Configure font family. (P1)
- Allow global
configuration of the font family of all visually
rendered text, with an option to override font families specified by the author
or by user agent defaults.
- Allow the user to choose from among the full range of font families
supported by the
operating environment.
Content only.
Checkpoint 4.2
Note: For example, allow the user to specify that all text is to be rendered in a particular
sans-serif font family. For text that
cannot be rendered properly using the user's preferred font family, the user
agent may substitute an alternative font family.
Who benefits:
- Users with low vision or some users with a cognitive disability or reading
disorder require the ability to change the font family of text in order to read
it.
Example techniques:
- Inherit font family information from user preferences specified for the
operating environment.
- Implement the
'font-family' property in CSS ([CSS2], section 15.2.2).
- Allow the user to override author-specified font families with differing
levels of detail. For instance, use font A in place of any sans-serif font and
font B in place of any serif font.
Doing more:
- Allow the user to configure font families on an element level (i.e., more
precisely than globally). User style sheets allow such detailed
configurations.
4.3
Configure text colors. (P1)
- Allow global
configuration of the foreground and background color of all visually
rendered
text, with an option to override
foreground and background colors specified by the author or user agent
defaults.
- Allow the user to choose from among the full range of colors supported by
the
operating environment.
Content only.
Checkpoint 4.3
Note: User configuration of foreground and background
colors may inadvertently lead to the inability to distinguish ordinary text
from selected text, focused text, etc. See checkpoint 10.3 for more information about highlight
styles.
Who benefits:
- Users with color deficiencies and some users with a cognitive
disability.
Example techniques:
- Inherit foreground and background color information from user preferences
specified for the
operating environment.
- Implement the
'color' and
'border-color' properties in CSS 2 ([CSS2], sections 14.1 and 8.5.2,
respectively).
- Implement the
'background-color' property (and other background properties) in CSS 2
([CSS2],
section 14.2.1).
- SMIL does not have a global property for "background color", but allows
specification of background color by region (refer, for example, to the
definition of the '
background-color
' attribute defined in section 3.3.1 of
SMIL 1.0
[SMIL]). In the case of SMIL, the user agent would satisfy this
checkpoint by applying the users preferred background color to all regions (and
to all root-layout
elements as well). SMIL 1.0 does not have a way
to specify the foreground color of text, so that portion of the checkpoint
would not apply.
- In SVG 1.0
[SVG], the 'fill' and 'stroke' properties are used to paint
foreground colors.
Doing more:
- Allow the user to specify minimal contrast between foreground and
background colors, adjusting colors dynamically to meet those
requirements.
Checkpoints for multimedia presentations and other
presentations that change continuously over time
4.4 Slow multimedia. (P1)
- Allow the user to slow the presentation rate of audio and animations (including video and animated
images).
- For a visual
track, provide at least one setting between 40% and 60% of the
original speed.
- For a prerecorded audio
track including audio-only presentations, provide at least one
setting between 75% and 80% of the original speed.
- When the user agent allows the user to slow the visual track of a
synchronized multimedia presentation to between 100% and 80% of its original
speed, synchronize the visual and audio tracks. Below 80%, the user agent is
not required to render the audio
track.
- The user agent is not required to satisfy this checkpoint for audio and
animations whose
recognized role is to create a purely stylistic effect.
Content only.
Checkpoint 4.4
Note: Purely stylistic effects include background sounds,
decorative animated images, and effects caused by style sheets. The style
exception of this checkpoint is based on the assumption that authors have
satisfied the requirements of the "Web Content Accessibility Guidelines 1.0"
[WCAG10] not to convey information through style alone (e.g.,
through color alone or style sheets alone). See checkpoint 2.6 and checkpoint 4.7.
Notes and rationale:
- Slowing one track (e.g., video) may make it harder for a user to understand
another synchronized track (e.g., audio), but if the user can understand
content after two passes, this is better than not being able to understand it
at all.
- Some formats (e.g., streaming formats), might not enable the user agent to
slow down playback and would thus be subject to applicability.
Who benefits:
- Some users with a learning or cognitive disability, or some users with
newly acquired sensory limitations (such as a person who is newly blind and
learning to use a screen reader). Users who have beginning familiarity with a
natural
language may also benefit.
Example techniques:
- When changing the rate of audio, avoid pitch distortion.
- HTML 4 [HTML4], background animations may
be specified with the deprecated
background
attribute.
- The
SMIL 2.0 Time Manipulations Module ([SMIL20], chapter 11) defines the
speed
attribute, which can be used to change the playback rate (as
well as forward or reverse direction) of any animation.
- Authors sometimes specify background sounds with the "bgsound" attribute.
Note: This attribute is not part of
HTML 4
[HTML4].
Doing more:
- Allowing the user to speed up audio is also useful. For example, some users
who access content serially benefit from the ability to speed up audio.
References:
- Refer to variable playback speed techniques used for Digital Talking Books
[TALKINGBOOKS].
4.5 Start, stop, pause, advance
multimedia. (P1)
- Allow the user to stop, pause, resume, fast advance, and fast reverse audio
and
animations (including video and animated
images) that last three or more seconds at their default playback rate.
- The user agent is not required to satisfy this checkpoint for audio and
animations whose
recognized role is to create a purely stylistic effect.
- The user agent is not required to play synchronized audio during fast
advance or reverse of animations (though doing so may help orient the
user).
- The user agent is not required to play animations during fast advance and
fast reverse.
- When the user pauses a real-time audio or animation, the user agent may
discard packets that continue to arrive during the pause.
Content only.
Checkpoint 4.5
Note: See
checkpoint 4.4 for more information about the exception for purely
stylistic effects. This checkpoint applies to content that is either rendered
automatically or on request from the user. The requirement of this checkpoint
is for control of each source of audio and animation that is recognized as distinct. Respect synchronization
cues per checkpoint
2.6.
Notes and rationale:
- Some formats (e.g., streaming formats), might not enable the user agent to
fast advance or fast reverse content and would thus be subject to
applicability.
- For some streaming media formats, the user agent might not be able to offer
some functionalities (e.g,. fast advance) when the content is being delivered
over the Web in real time. However, the user agent is expected to offer these
functionalities for content (in the same format) that is fully available, for
example on the user's computer.
Who benefits:
- Some users with a cognitive disability. Some users with a physical
disability who may not have fine control over advance and rewind
functionalities will find useful the ability to advance or rewind the
presentation in (configurable) increments.
Example techniques:
- If buttons are used to control advance and rewind, make the advance/rewind
distances proportional to the time the user activates the button. After a
certain delay, accelerate the advance/rewind.
- The
SMIL 2.0 Time Manipulations Module ([SMIL20], chapter 11) defines the
speed
attribute, which can be used to change the playback
direction (forward or reverse) of any animation. See also the
accelerate
and decelerate
attributes.
- Some content lends itself to different forward and reverse functionalities.
For instance, compact disk players often let listeners fast forward and
reverse, but also skip to the next or previous song.
Doing more:
- The user agent should display time codes or represent otherwise position in
content to orient the user.
- Apply techniques for changing audio speed without introducing
distortion.
- Alert the user whenever pausing the user agent may lead to packet
loss.
References:
- Refer to fast advance and fast reverse techniques used for Digital Talking
Books
[TALKINGBOOKS].
- Home Page Reader
[HPR] lets users insert bookmarks in presentations.
4.6 Position captions. (P1)
- For graphical
viewports, allow the user to position captions
with respect to synchronized visual
tracks as follows:
- if the user agent satisfies this checkpoint by using a markup language or
style sheet language to provide configuration or control, then the user agent
must allow the user to choose from among at least the range of positions
enabled by the format
- otherwise the user agent must allow both non-overlapping and overlapping
positions (e.g., by rendering captions in a separate
viewport that may be positioned on top of the visual track).
- In either case, the user agent must allow the user to override the author's specified position.
- The user agent is not required to change the layout of other content (i.e.,
reflow) after the user has changed the position of captions.
- The user agent is not required to make the captions background transparent
when those captions are rendered above a related video track.
Content only.
Checkpoint 4.6
Notes and rationale:
- One good reasons to render captions in an independent viewport is to allow
users with screen access programs to focus on them.
- Traditionally, captions have a background, and research shows that some
users prefer a black background behind white lettering is preferred.
Who benefits:
- Some users (e.g., with a cognitive disability) may need to be able to
position captions, etc. so that they do not obscure other content or are not
obscured by other content. Other users (e.g., users with a screen magnifier)
may require pieces of content to be in a particular relation to one another,
even if this means that some content will obscure other content.
Example techniques:
- User agents should implement the positioning features of the employed
markup or style sheet language. Even when a markup language does not specify a
positioning mechanism, when a user agent can recognize distinct text
transcripts,
collated text transcripts, or captions,
the user agent should allow the user to reposition them. User agents are not
required to allow repositioning when the captions, etc. cannot be separated
from other media (e.g., the captions are part of the video track).
- For the purpose of applying this clause, SMIL 1.0 [SMIL] user agents should recognize
as captions any media object whose reference from SMIL is guarded by the
'
system-captions
' test attribute.
- Implement the CSS 2
'position' property ([CSS2], section 9.3.1).
- Allow the user to choose whether captions appear at the bottom or top of
the video area or in other positions. Currently authors may place captions
overlying the video or in a separate box. Captions prevent users from being
able to view other information in the video or on other parts of the screen,
making it necessary to move the captions in order to view all content at once.
In addition, some users will find captions easier to read if they can place
them in a location best suited to their reading style.
- Allow users to configure a general preference for caption position and to
be able to fine tune specific cases. For example, the user may want the
captions to be in front of and below the rest of the presentation.
- Allow the user to drag and drop the captions to a place on the screen. To
ensure device-independence, allow the user to enter the screen coordinates of
one corner of the caption.
- Do not require users to edit the source code of the presentation to achieve
the desired effect.
Doing more:
- The user agent may allow configuration for transparent backgrounds. Refer
to checkpoint 4.3 for
requirements related to the control of text background colors.
- Allow the user to position all parts of a presentation rather than trying
to identify captions specifically (i.e., solving the problem generally may be
easier than for captions alone).
- Allow the user to resize (graphically) the captions, etc.
4.7 Slow other multimedia. (P2)
- Allow the user to slow the presentation rate of audio and animations (including video and animated
images) not covered by
checkpoint 4.4.
- The same speed percentage requirements of checkpoint 4.4 apply.
Content only.
Checkpoint 4.7
Note: User agents automatically satisfy this checkpoint if
they satisfy checkpoint 4.4
for all audio and animations.
4.8 Control other multimedia.
(P2)
- Allow the user to stop, pause, resume, fast advance, and fast reverse audio
and
animations (including video and animated
images) not covered by
checkpoint 4.5.
Content only.
Checkpoint 4.8
Note: User agents automatically satisfy this checkpoint if
they satisfy checkpoint
4.5 for all audio and animations.
Checkpoints for audio volume control
4.9 Global volume control. (P1)
- Allow global
configuration and control of
the volume of all audio, with an option to
override audio volumes specified by the author or user agent
defaults.
- The user must be able to choose zero volume (i.e.,
silent).
Content only.
Checkpoint 4.9
Note: User agents should allow configuration and control of
volume through available
operating environment controls.
Example techniques:
- Use audio control mechanisms provided by the
operating environment. Control of volume mix is particularly
important, and the user agent should provide easy access to those mechanisms
provided by the operating environment.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
- Implement the
'display',
'play-during', and
'speak' properties in CSS 2 ([CSS2], sections 9.2.5, 19.6, and
19.5, respectively).
- Authors sometimes specify background sounds with the "bgsound" attribute.
Note: This attribute is not part of
HTML 4
[HTML4].
Who benefits:
- Users who are hard of hearing or who rely on audio and synthesized speech.
Users in a noisy environment will also benefit.
References:
- Refer to guidelines for audio characteristics used for Digital Talking
Books
[TALKINGBOOKS].
4.10 Independent volume control.
(P1)
- Allow independent control of
the volumes of distinct audio sources synchronized to play simultaneously. The
user agent is not required to satisfy this checkpoint for audio whose recognized role is to create a purely stylistic
effect.
Content only.
Checkpoint 4.10
Note: See
checkpoint 4.4 for more information about the exception for purely
stylistic effects. The user agent should satisfy this checkpoint by allowing
the user to control independently the volumes of all distinct audio sources
(e.g., by implementing a general audio mixer type of functionality). The user
control required by this checkpoint includes the ability to override author-specified volumes for the
relevant sources of audio. See also checkpoint 4.13.
Notes and rationale:
- Sounds that play at different times are distinguishable and therefore
independent control of their volumes is not required by this checkpoint (since
volume control required by checkpoint 4.9 suffices).
- There are at least three good reasons for strongly recommending that all
sounds be independently configurable, not just those synchronized to play
simultaneously.
- sounds that are not synchronized may end up playing simultaneously;
- if the user cannot anticipate when a sound will play, the user cannot
adjust the global volume control at appropriate times to affect this
sound;
- it is extremely inconvenient to have to adjust the global volume
frequently.
Who benefits:
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech.
Related techniques:
- For each source of audio recognized as distinct, allow the user to control
the volume using the same user interface used to satisfy the requirements of checkpoint 4.5.
4.11
Control other volume. (P2)
- Allow independent control of
the volumes of distinct audio sources synchronized to play simultaneously that
are not covered by
checkpoint 4.10.
Content only.
Checkpoint 4.11
Note: User agents automatically satisfy this checkpoint if
they satisfy
checkpoint 4.10 for all audio.
Checkpoints for synthesized speech
See also techniques for synthesized
speech.
4.12 Configure speech rate. (P1)
- Allow
configuration and control of
the synthesized speech rate, according to the full range offered by the speech
synthesizer.
Content only.
Checkpoint 4.12
Note: The range of speech rates offered by the speech
synthesizer may depend on natural language.
Example techniques:
- For example, many speech synthesizers offer a range for English speech of
120 - 500 words per minute or more. The user should be able to increase or
decrease the speech rate in convenient increments (e.g., in large steps, then
in small steps for finer control).
- User agents may allow different speech rate configurations for different
natural languages. For example, this may be implemented with CSS2 style sheets
using the :lang
pseudo-class ([CSS2], section 5.11.4).
- Use synthesized speech mechanisms provided by the
operating environment.
- Implement the CSS 2
'speech-rate' property ([CSS2], section 19.8).
Who benefits:
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech.
Doing more:
- Content may include commands that are interpreted by a speech engine to
change the speech rate (or control other speech parameters). This checkpoint
does not require the user agent to allow the user to override author-specified
speech rate changes (e.g., by transforming or otherwise stripping out these
commands before passing on the content to the speech engine). Speech engines
themselves may allow user override of author-specified speech rate changes. For
these such speech engines, the user agent should ensure access to this feature
as part of satisfying this checkpoint.
4.13 Configure speech volume.
(P1)
- Allow
control of the synthesized speech volume,
independent of other sources of audio.
Content only.
Checkpoint 4.13
Note: The user control required by this checkpoint includes
the ability to override
author-specified speech volume. See also checkpoint 4.10.
Example techniques:
- The user agent should allow the user to make synthesized speech louder and
softer than other audio sources.
- Use synthesized speech mechanisms provided by the
operating environment.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
Who benefits:
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech.
4.14 Configure speech
characteristics. (P1)
- Allow
configuration of speech characteristics according to the full range
of values offered by the speech synthesizer.
Content only.
Checkpoint 4.14
Note: Some speech synthesizers allow users to choose values
for speech characteristics at a higher abstraction layer, i.e., by choosing
from present options that group several characteristics. Some typical options
one might encounter include: "adult male voice", "female child voice", "robot
voice", "pitch", "stress", etc. Ranges for values may vary among speech
synthesizers.
Example techniques:
- Use synthesized speech mechanisms provided by the
operating environment.
- One example of a speech API is Microsoft's Speech Application
Programming Interface
[SAPI].
-
Who benefits:
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech.
References:
- For information about these speech characteristics, please refer to
descriptions in section 19.8 of Cascading Style Sheets Level 2 [CSS2].
4.15 Specific speech characteristics.
(P2)
- Allow
configuration of the following speech characteristics: pitch, pitch
range, stress, richness.
- Pitch refers to the average frequency of the speaking voice.
- Pitch range specifies a variation in average frequency.
- Stress refers to the height of "local peaks" in the intonation contour of
the voice.
- Richness refers to the richness or brightness of the voice.
Content only.
Checkpoint 4.15
Note: This checkpoint is more specific than checkpoint
4.14: it requires support for the voice characteristics listed. Definitions
for these characteristics are taken from section 19 of the Cascading Style
Sheets Level 2 Recommendation [CSS2]; please refer to that
specification for additional
informative descriptions. Some speech synthesizers allow users to
choose values for speech characteristics at a higher abstraction layer, i.e.,
by choosing from present options distinguished by "gender", "age", "accent",
etc. Ranges of values may vary among speech synthesizers.
4.16 Configure speech features.
(P2)
- Provide support for
user-defined extensions to the speech dictionary, as well as the following
functionalities:
- spell-out: spell text one character at a time or according to
language-dependent pronunciation rules;
- speak-numeral: speak a numeral as individual digits or as a full number;
and
- speak-punctuation: speak punctuation literally or render as natural
pauses.
Content only.
Checkpoint 4.16
Note: Definitions for the functionalities listed are taken
from section 19 of the Cascading Style Sheets Level 2 Recommendation [CSS2]; please refer
to that specification for additional
informative descriptions.
Example techniques:
-
Who benefits:
- Users (e.g., with blindness or low vision) who rely on audio and
synthesized speech.
References:
- For information about these functionalities, please refer to descriptions
in section 19.8 of Cascading Style Sheets Level 2 [CSS2].
Checkpoints related to style sheets
4.17
Choose style sheets. (P1)
- For user agents that support
style sheets, allow the user to choose from (and apply) available
author and
user style sheets or to ignore them.
Both content and user agent.
Checkpoint 4.17
Note: By definition, the user agent's default style sheet is always
present, but may be overridden by author or user styles. Developers should not
consider that the user's ability to turn off author and user style sheets is an
effective way to improve content accessibility; turning off style sheet support
means losing the many benefits they offer. Instead, developers should provide
users with finer control over user agent or content behavior known to raise
accessibility barriers. The user should only have to turn off author and user
style sheets as a last resort.
Example techniques:
- For HTML [HTML4], make available "class" and
"id" information so that users can override styles.
- Implement user style
sheets.
- Implement the
"!important" semantics of CSS 2 ([CSS2], section 6.4.2).
Who benefits:
- Any user with a disability who needs to override the author's style sheets
or user agent default style sheets in order to have control over style and
presentation, or who needs to tailor the style of rendered content to meet
their own needs.
References:
- For information about how alternative style sheets are specified in HTML 4
[HTML4],
please refer to
section 14.3.1.
- For information about how alternative style sheets are specified in XML 1.0
[XML], please
refer to "Associating Style Sheets with XML documents Version 1.0"
[XMLSTYLE].
Checkpoints
5.1 No automatic content focus change.
(P2)
- Allow
configuration so that if a viewport
opens without explicit
user request, its content
focus does not automatically become the
current focus.
- Configuration is preferred, but is not required if the content focus can
only ever be moved on explicit
user request.
Both content and user agent.
Checkpoint 5.1
Who benefits:
- Moving the focus automatically (and unexpectedly) to a new viewport may
disorient some users with a cognitive disability, blindness, or low vision.
These users may find it difficult to restore the previous point of regard.
Example techniques:
- Allow the user to configure how the
current focus changes when a new viewport opens. For instance, the
user might choose between these two options:
- Do not change the focus when a viewport opens, but alert the user (e.g.,
with a beep, flash, and text message on the status bar). Allow the user to
navigate directly to the new window upon demand.
- Change the focus when a window opens and use a subtle alert (e.g., a beep,
flash, and text message on the status bar) to indicate
that the focus has changed.
- If a new viewport
or prompt appears but focus does not move to it, alert assistive technologies
(per checkpoint 6.5) so that they
may discreetly inform the user.
- When a viewport is duplicated, the focus in the new viewport should
initially be the same as the focus in the original viewport. Duplicate
viewports allow users to navigate content (e.g., in search of some information)
in one viewport while allowing the user to return with little effort to the
point of regard in the duplicate viewport. There are other techniques for
accomplishing this (e.g., "registers" in Emacs).
- In JavaScript, the focus may be changed with
myWindow.focus();
- For user agents that implement CSS 2 [CSS2], the following rule will
generate a message to the user at the beginning of link text for links that are
meant to open new windows when followed:
A[target=_blank]:before{content:"Open new window"}
Doing more:
- The user agent may also allow configuration about whether the pointing
device moves automatically to windows that open without an explicit user
request.
5.2 Keep viewport on top. (P2)
- For graphical user interfaces, allow
configuration so that the viewport with the
current focus remains "on top" of all
other viewports with which it overlaps.
Both content and user agent.
Checkpoint 5.2
Notes and rationale:
- The alert is important to ensure that the user realizes a new viewport has
opened; the new viewport may be hidden by the viewport configured to remain on
top.
- In most operating environments, the viewport with focus is generally the
viewport "on top". In some environments, it's possible to allow a viewport that
is not on top to have focus.
Who benefits:
- Some users with a cognitive disability may find it disorienting if the
viewport being viewed unexpectedly changes.
Doing more:
- The user agent may also allow configuration about whether the viewport
designated by the pointing device always remains on top.
5.3 Manual viewport open only. (P2)
- Allow
configuration so that viewports only open on explicit
user request.
- In this configuration, instead of opening a viewport automatically, alert
the user and allow the user to open it on demand (e.g., by following a link or
confirming a prompt).
- Allow the user to close viewports.
- If a viewport (e.g., a frame set) contains other viewports, these
requirements only apply to the outermost container viewport.
- Configuration is preferred, but is not required if viewports can only ever
open on explicit
user request.
Both content and user agent.
Checkpoint 5.3
Note: User creation of a new viewport (e.g., empty or with
a new resource loaded) through the user agent's user interface constitutes an
explicit user request. See also checkpoint 5.1 (for control over changes of focus when a
viewport opens) and checkpoint 6.5
(for programmatic alert of changes to the user interface).
Who benefits:
- Navigation of multiple open viewports may be difficult for some users who
navigate viewports serially (e.g., users with visual or physical disabilities)
and for some users with a cognitive disability (as it may disorient them).
Example techniques:
- For HTML [HTML4], allow the user to control
the process of opening a document in a new "target" frame or a viewport created
by a script. For example, for
target="_blank"
, open the window
according to the user's preference.
- For SMIL
[SMIL], allow the user to control viewports created with the
"
new
" value of the "show
" attribute.
- In JavaScript, windows may be opened with:
myWindow.open("example.com", "My New Window");
myWindow.showHelp(URI);
5.4 Selection and focus in viewport.
(P2)
- Ensure that when a viewport's selection
or content
focus changes, it is at least partially in the viewport after the change.
Both content and user agent.
Checkpoint 5.4
Note: For example, if users navigating links move to a
portion of the document outside a graphical viewport, the viewport should
scroll to include the new location of the focus. Or, for users of audio
viewports, allow configuration to render the selection or focus immediately
after the change.
Who benefits:
- Users who may be disoriented by a change in focus or selection that is not
reflected in the viewport. This includes some users with blindness or low
vision, and some users with a cognitive disability.
Example techniques:
- There are times when the content focus changes (e.g., link navigation) and
the viewport should move to track it. There are other times when the viewport
changes position (e.g., scrolling) and the content focus is moved to follow it.
In both cases, the focus (or selection) is in the viewport after the
change.
- If a search causes the selection or focus to change, ensure that the found
content is not hidden by the search prompt.
- When the content focus changes, register the newly focused element in the
navigation sequence; sequential navigation should start from there.
- Unless viewports have been coordinated, changes to selection or focus in
one viewport should not affect the selection or focus in another viewport.
- The persistence of the selection or focus in the viewport will vary
according to the type of viewport. For any viewport with persistent rendering
(e.g., a two-dimensional graphical or tactile viewport), the focus or selection
should remain in the viewport after the change until the user changes the
viewport. For any viewport without persistent rendering (e.g., and audio
viewport), once the focus or selection has been rendered, it will no longer be
"in" the viewport. In a pure audio environment, the whole persistent context is
in the mind of the user. In a graphical viewport, there is a large shared
buffer of dialog information in the display. In audio, there is no such
sensible patch of interaction that is maintained by the computer and accessed,
ad lib, by the user. The audio rendering of content requires the elapse of
time, which is a scarce resource. Consequently, the flow of content through the
viewport has to be managed more carefully, notably when the content was
designed primarily for graphical rendering.
- If the rendered selection or focus does not fit entirely within the limits
of a graphical viewport:
- if the region actually displayed prior to the change was within the
selection or focus, do not move the viewport.
- otherwise, if the region actually displayed prior to the change was not
within the newly selected or focused content, move to display at least the
initial fragment of such content.
5.5 Confirm form submission. (P2)
- Allow
configuration to prompt the
user to confirm (or cancel) any form submission.
- Configuration is preferred, but it not required if forms can only ever be
submitted on explicit
user request.
Content only.
Checkpoint 5.5
Note: For example, do not submit a form automatically when
a menu option is selected, when all fields of a form have been filled out, or
when a "mouseover" or "change" event occurs.
Example techniques:
- In HTML 4
[HTML4], form submit controls are the
INPUT element (section 17.4) with
type="submit"
and
type="image"
, and the
BUTTON element (section 17.5) with type="submit"
.
- Allow the user to configure script-based submission (e.g., form submission
accomplished through an "onChange" event). For instance, allow these settings:
- Do not allow script-based submission.
- Allow script-based submission after confirmation from the user.
- Allow script-based submission without prompting the user (but not by
default).
- Authors may write scripts that submit a form when particular events occur (e.g., "onchange" events). Be
aware of this type of practice:
<SELECT NAME="condition" onchange="switchpage(this)">
As soon as the user attempts to navigate the menu, the "switchpage" function
opens a document in a new viewport. Try to avoid orientation problems that may
be caused by scripts bound to form elements.
- Be aware that users may inadvertently pressing the Return or
Enter key and accidentally submit a form.
- In JavaScript, a form may be submitted with:
document.form[0].submit();
document.all.mySubmitButton.click();
- Generate a form submit button when the author has not provided one.
Who benefits:
- Any user who might be disoriented by an automatic form submission (e.g.,
users with blindness who are are navigating serially through select box
options, or some users with a cognitive disability) or who might inadvertently
submit a form (e.g., some users with a physical disability).
Doing more:
- Some users may not want to have to confirm all form submissions, so allow
multiple configurations, such as: confirm all form submissions; confirm
script-activated form submissions; confirm all form submissions except those
done through the graphical user interface (e.g., when the user moves
content focus to a submit button and
activates it); etc.
- Users who navigate a document serially may think that the submit button in
a form is the "last" control
they need to complete before submitting the form. Therefore, for forms in which
additional controls follow a submit button, if those controls have not been
completed, inform the user and ask for confirmation (or completion) before
submission.
- For forms, allow users to search for controls
that need to be changed by the user before submitting the form.
5.6 Confirm fee links. (P2)
- Allow
configuration to prompt the
user to confirm (or cancel) any payment that results from activation of a fee
link.
- Configuration is preferred, but is not required if fee links can only ever
be activated on explicit
user request.
Content only. Checkpoint
5.6
Who benefits:
- Any user who might inadvertently activate a fee link (e.g., some users with
a physical or cognitive disability).
Example techniques:
- Allow the user to configure the user agent to prompt for payments above a
certain amount (including any payment).
- Warn the user that even in this configuration, the user agent may not be
able to recognize some payment mechanisms.
5.7
Manual viewport close only. (P3)
- Allow
configuration to prompt the
user to confirm (or cancel) closing any viewport that starts to close without
explicit
user request.
User agent only.
Checkpoint 5.7
Who benefits:
- Some users with a cognitive disability may find it disorienting if a
viewport closes automatically. On the other hand, some users with a physical
disability may wish these same viewports to close automatically (rather than
being required to close them manually).
Example techniques:
- In JavaScript, windows may be closed with
myWindow.close();
Checkpoints
6.1 DOM read access. (P1)
- Provide programmatic read access to HTML and
XML content by
conforming to the following modules of the W3C Document Object Model DOM Level 2 Core Specification
[DOM2CORE] and exporting the interfaces they define:
- the Core module for HTML;
- the Core and XML modules for XML.
Content only.
Checkpoint 6.1
Note: Please refer to the "Document Object Model (DOM)
Level 2 Core Specification" [DOM2CORE] for information about
HTML and XML versions covered.
Notes and rationale:
- The primary reason for requiring user agents to implement the DOM is that
this gives assistive technologies access to the original structure of the
document. For example, this means that assistive technologies that render
content as speech are not required to construct the speech view by "reverse
engineering" a graphical view. Direct access to the structure allows the
assistive technologies to render content in a manner best suited to a
particular output device. This does not mean that assistive technologies should
be prevented from having access to the rendering of the conforming user agent;
simply that they not be required to depend entirely on it. In fact, speech user
agents may wish to synchronize a graphical view with a speech view.
- Note that the W3C DOM is designed to be used on a server as well as a
client and does not address some user interface-specific information.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Example techniques:
- Refer to a listing of DOM implementations at the Open
Directory Project [ODP-DOM].
Related techniques:
- See the appendix on loading assistive technologies
for DOM access.
References:
- For information about rapid access to Internet Explorer's [IE-WIN] DOM
through COM, refer to
[BHO].
- Refer to the DirectDOM Java implementation of the DOM
[DIRECTDOM].
6.2 DOM write access. (P1)
- If the user can modify HTML and XML content through the
user interface, provide the same
functionality programmatically by conforming to the following modules of the
W3C Document Object Model DOM
Level 2 Core Specification [DOM2CORE] and exporting the
interfaces they define:
- the Core module for HTML;
- the Core and XML modules for XML.
Content only.
Checkpoint 6.2
Note: For example, if the user interface allows users to
complete HTML forms, this must also be possible through the
required DOM APIs. Please refer to the "Document Object
Model (DOM) Level 2 Core Specification" [DOM2CORE]
for information about HTML and XML
versions covered.
Notes and rationale:
- Allowing assistive technologies write access through the DOM allows them
to:
- modify the attribute list of a document and thus add information into the
document object that will not be rendered by the user agent.
- add entire nodes to the document that are specific to the assistive
technologies and that may not be rendered by a user agent unaware of their
function.
- The ability to write to the DOM can improve performance for the assistive
technology. For example, if an assistive technology has already traversed a
portion of the document object and knows that a section (e.g., a style element)
could not be rendered, it can mark this section "to be skipped".
- Another benefit is to add information necessary for audio rendering but
that would not be stored directly in the DOM during parsing (e.g., numbers in
an ordered list). An assistive technology component can add numeric information
to the document object. The assistive technology can also mark a subtree as
having been traversed and updated, to eliminate recalculating the information
the next time the user visits the subtree.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Related techniques:
- See also techniques for
checkpoint 6.1.
6.3 Programmatic access to other
content. (P1)
- For markup languages other than HTML and
XML, provide programmatic read access to
content.
- Provide programmatic write access for those parts of content that the user
can modify through the user interface. To satisfy these requirements, implement
at least one API that is either
- defined by a W3C Recommendation, or
- a publicly documented API designed to enable interoperability with
assistive technologies.
- If no such API is available, or if available APIs do not enable the user
agent to satisfy the requirements, implement at least one publicly documented
API to satisfy the requirements, and follow operating environment
conventions for the use of input and output
APIs.
Content only.
Checkpoint 6.3
Note: This checkpoint addresses content not covered by
checkpoints checkpoint 6.1
and checkpoint 6.2. An API
is considered "available" if the specification of the API is published (e.g.,
as a W3C Recommendation) in time for integration into a user agent's
development cycle.
Notes and rationale:
- Some examples of markup languages covered by this checkpoint include
SGML
applications other than HTML and
RTF, and TeX.
- Some software (e.g., Word and Excel for Windows) offer APIs specific to
their formats.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Related techniques:
- See techniques for checkpoint
6.4.
References:
- Some public APIs that enable access include:
- Microsoft Active Accessibility ([MSAA]) in Windows 95/98/NT
versions.
- Sun Microsystems Java Accessibility API ([JAVAAPI]) in Java JDK. If the
user agent supports Java applets and provides a Java Virtual Machine to run
them, the user agent should support the proper loading and operation of a Java
native assistive technology. This assistive technology can provide access to
the applet as defined by Java accessibility standards.
6.4 Programmatic operation. (P1)
- Provide programmatic read access to user
agent user interface controls.
- Provide programmatic write access for those controls that the user can
modify through the user interface. For security reasons, user agents are not
required to allow instructions in content to
modify user agent user interface controls.
- To satisfy these requirements, implement at least one
API that is either
- defined by a W3C Recommendation, or
- a publicly documented API designed to enable interoperability with
assistive technologies.
- If no such API is available, or if available APIs do not enable the user
agent to satisfy the requirements, implement at least one publicly documented
API that allows programmatic operation of all of the functionalities that are
available through the user agent user interface, and follow operating
environment
conventions for the use of input and output
APIs.
User agent only.
Checkpoint 6.4
Note: APIs used to satisfy the requirements of this
checkpoint may be platform-independent APIs such as the W3C
DOM, conventional APIs for a particular operating environment, conventional
APIs for programming languages, plug-ins,
virtual machine environments, etc. User agent developers are encouraged to
implement APIs that allow assistive technologies to interoperate with multiple
types of software in a given operating environment (user agents, word
processors, spreadsheet programs, etc.), as this reuse will benefit users and
assistive technology developers. User agents should always follow operating
environment conventions for the use of input and output APIs. An API is
considered "available" if the specification of the API is published (e.g., as a
W3C Recommendation) in time for integration into a user agent's development
cycle.
Notes and rationale:
- It is important to use APIs that ensure that
text content is available to assistive technologies as text and not,
for example, as a series of strokes drawn on the screen.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Example techniques:
- User agents that implement conventional APIs are
generally more compatible with assistive technologies and provide accessibility
at no extra cost.
- Use conventional user
interface controls. Third-party assistive technology developers are
more likely able to access conventional controls than custom controls. If you use custom controls, review
them for accessibility and compatibility with third-party assistive technology.
Ensure that they provide accessibility information through an API as is done
for the conventional controls.
- Make use of
operating environment-level features. See the appendix of accessibility features for some common
operating systems.
- Operating system and application frameworks have conventions for
communication with input devices. In the case of Windows, OS/2, the X Windows
System, and Mac OS, the window manager provides Graphical User Interface
(GUI) applications with this information through the
messaging queue. In the case of non-GUI applications, the compiler run-time
libraries provide conventional mechanisms for receiving keyboard input in the
case of desktop operating systems. If you use an application framework such as
the Microsoft Foundation Classes, the framework used should support the same
conventional input mechanisms.
- Do not communicate directly with an input device; this may circumvent
operating environment messaging. For instance, in Windows, do not
open the keyboard device driver directly. It is often the case that the
windowing system needs to change the form and method for processing
conventional input mechanisms for proper application coexistence within the
user interface framework.
- Do not implement your own input device event queue mechanism; this may
circumvent operating environment messaging. Some assistive technologies use
conventional system facilities for simulating keyboard and mouse events. From
the application's perspective, these events are no different than those
generated by the user's actions. The "Journal Playback Hooks" (in both OS/2 and
Windows) are one example of an application that feeds the standard event
queues. For an example of a standard event queue mechanism, refer to the
"Carbon Event Manager Preliminary API Reference" [APPLE-HI].
-
Operating environments have conventions for communicating with
output devices. In the case of common desktop operating systems such as
Windows, OS/2, and Mac OS, conventional APIs are provided for writing to the display
and the multimedia subsystems.
- Avoid rendering text in the
form of a bitmap before transferring to the screen, since some screen readers
rely on the user agent's offscreen model. An offscreen model is rendered
content created by an assistive technology that is based on the rendered
content of another user agent. Assistive technologies that rely on
an offscreen model generally construct it by intercepting conventional
operating environment drawing calls. For example, in the case of
display drivers, some screen readers are designed to monitor what is drawn on
the screen by hooking drawing calls at different points in the drawing process.
While knowing about the user agent's formatting may provide some useful
information to assistive technologies, this document encourages assistive
technologies to access to content directly through published APIs (such as the
DOM) rather than via a particular rendering.
- Common operating environment two-dimensional graphics engines and drawing
libraries provide functions for drawing text to the
screen. Examples of this are the Graphics Device Interface (GDI) for Windows,
Graphics Programming Interface (GPI) for OS/2, and the X library (XLIB) for the
X Windows System or Motif.
- Do not communicate directly with an output device.
- Do not draw directly to the video frame buffer.
- Do not provide your own mechanism for generating pre-defined
operating environment sounds.
- When writing textual information in a GUI
operating environment, use conventional operating environment APIs for drawing text.
- Use
operating environment resources for rendering audio information.
When doing so, do not take exclusive control of system audio resources. This
could prevent an assistive technology such as a screen reader from speaking if
they use software text-to-speech conversion. Also, in operating environments
like Windows, a set of audio sound resources is provided to support
conventional sounds such as alerts. These
preset sounds are used to trigger SoundSentry
graphical cues when a problem occurs; this benefits users with hearing
disabilities. These cues may be manifested by flashing the desktop, active
caption bar, or current viewport. It is important to use the conventional
mechanisms to generate audio feedback so that operating environments or special
assistive technologies can add additional functionality for users with hearing
disabilities.
- API designers should promote backwards compatibility so that assistive
technologies do not suddenly break when a new version of an API is published
and implemented by user agents.
References:
- Some public accessibility APIs include:
- Microsoft Active Accessibility ([MSAA]). This the conventional
accessibility API for the Windows 95/98/NT operating systems.
- Sun Microsystems Java Accessibility API ([JAVAAPI]) in the Java JDK. This
is the conventional accessibility API for the Java environment. If the user
agent supports Java applets and provides a Java Virtual Machine to run them,
the user agent should support the proper loading and operation of a Java native
assistive technology. This assistive technology can provide access to the
applet as defined by Java accessibility standards.
- For information about rapid access to Internet Explorer's [IE-WIN] DOM
through COM, refer to Browser Helper Objects [BHO].
6.5 Programmatic alert of changes. (P1)
- Provide programmatic alert of changes to
content, user
interface controls,
selection, content
focus, and user
interface focus.
- To satisfy these requirements, implement at least one
API that is either
- defined by a W3C Recommendation, or
- a publicly documented API designed to enable interoperability with
assistive technologies.
- If no such API is available, or if available APIs do not enable the user
agent to satisfy the requirements, implement at least one publicly documented
API to satisfy the requirements, and follow operating environment
conventions for the use of input and output
APIs.
Both content and user agent. Checkpoint
6.5
Note: For instance, when user interaction in one frame
causes automatic changes to content in another, provide a programmatic alert.
An API is considered "available" if the specification of the API is published
(e.g., as a W3C Recommendation) in time for integration into a user agent's
development cycle.
Who benefits:
- Users with a disability who rely on assistive technologies for output.
Example techniques:
- Write output to and take input from conventional
operating environment APIs rather than directly
from hardware controls. This will enable the input/output to be redirected from
or to assistive technology devices – for example, screen readers and
braille displays often redirect output (or copy it) to a serial port, while
many devices provide character input, or mimic mouse functionality. The use of
generic APIs makes this feasible in a way that allows for interoperability of
the assistive technology with a range of applications.
- Alert the user when an action in one frame causes the content of another
frame to change. Allow the user to navigate with little effort to the frame(s)
that changed.
Related techniques:
- See techniques for checkpoint
6.4.
References:
- Refer to "mutation events" in "Document Object Model (DOM) Level 2 Events
Specification" [DOM2EVENTS]. This DOM Level 2
specification allows assistive technologies to be informed of changes to the
document tree.
- Refer also to information about monitoring HTML events
through the document
object model in Internet Explorer [IE-WIN].
6.6 Conventional keyboard APIs. (P1)
- Follow
operating environment conventions when implementing
APIs for the keyboard.
- If such APIs for the keyboard do not exist, implement
publicly documented APIs for the keyboard.
User agent only. Checkpoint
6.6
Note: An operating environment may define more than one
conventional API for the keyboard. For instance, for Japanese and Chinese,
input may be processed in two stages, with an API for each.
Who benefits:
- Users with a disability who rely on assistive technologies for input.
Example techniques:
- Account for author-specified keyboard bindings, such as those specified by
"accesskey" attribute in HTML 4 ([HTML4], section
17.11.2).
- Test that all user
interface components may be operable by software or devices that
emulate a keyboard. Use SerialKeys and/or voice
recognition software to test keyboard event emulation.
Related techniques:
- Apply the techniques for checkpoint 1.1 to the keyboard.
Doing more:
- Enhance the functionality of conventional operating environment controls to
improve accessibility where none is provided by responding to conventional
keyboard input mechanisms. For example provide keyboard navigation to menus and
dialog box controls in the Apple Macintosh operating system. Another example is
the Java Foundation Classes, where internal frames do not provide a keyboard
mechanism to give them focus. In this case, you will need to add keyboard
activation through the conventional keyboard activation facility for Abstract
Window Toolkit components.
6.7 API character encodings. (P1)
- For an API implemented to satisfy requirements of this document, support
the character
encodings required for that API.
Both content and user agent.
Checkpoint 6.7
Note: Support for character encodings is important so that
text is not "broken" when communicated to assistive technologies. For example,
the DOM Level 2 Core Specification [DOM2CORE], section 1.1.5
requires that the DOMString
type be encoded using UTF-16. This
checkpoint is an important special case of the other API
requirements of this document.
Who benefits:
- Users with disabilities who rely on assistive technologies for input and
output.
Example techniques:
- The list of character encodings that any conforming implementation of Java
version 1.3
[JAVA13] must support is: US-ASCII, ISO-8859-1, UTF-8, UTF-16BE,
UTF-16LE, and UTF-16.
- MSAA [MSAA] relies on the
COM interface, which in turn relies on Unicode [UNICODE],
which means that for MSAA a user agent must support UTF-16. From Chapter 3 of
the COM documentation, on interfaces, entitled "Interface Binary Standard":
Finally, and quite significantly, all strings passed through all COM
interfaces (and, at least on Microsoft platforms, all COM APIs) are Unicode
strings. There simply is no other reasonable way to get interoperable objects
in the face of (i) location transparency, and (ii) a high-efficiency object
architecture that doesn't in all cases intervene system-provided code between
client and server. Further, this burden is in practice not large."
6.8 DOM CSS access. (P2)
- For user agents that implement
Cascading Style Sheets (CSS), provide programmatic access to
those style sheets by conforming to the CSS module of the W3C Document Object
Model (DOM) Level 2 Style
Specification [DOM2STYLE] and exporting the
interfaces it defines.
Content only.
Checkpoint 6.8
Note: As of the publication of this document, Cascading
Style Sheets (CSS) are defined by CSS Level 1 [CSS1] and CSS Level
2 [CSS2].
Please refer to the "Document Object Model (DOM) Level 2 Style Specification"
[DOM2STYLE] for information
about CSS versions covered.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Related techniques:
- See techniques for
6.9 Timely access. (P2)
- Ensure that programmatic exchanges proceed in a timely manner.
Both content and user agent.
Checkpoint 6.9
Note: For example, the programmatic exchange of information
required by other checkpoints in this document should be efficient enough to
prevent information loss, a risk when changes to content or user interface
occur more quickly than the communication of those changes. Timely exchange is
also important for the proper synchronization of alternative renderings. The
techniques for this checkpoint explain how developers can reduce communication
delays. This will help ensure that assistive technologies have timely access to
the document
object model and other information that is important for providing
access.
Who benefits:
- Users with a disability who rely on assistive technologies for input and
output.
Related techniques:
- Please see the appendix that explains how to load
assistive technologies for DOM access.
Doing more:
- Alert the user when information may be lost due to communication
delays.
Checkpoints
7.1 Focus and selection conventions.
(P1)
- Follow
operating environment conventions that benefit accessibility when implementing the
selection, content
focus, and user
interface focus.
User agent only.
Checkpoint 7.1
Note: This checkpoint is an important special case of checkpoint 7.3. See also checkpoint 9.1 and checkpoint 9.2.
Who benefits:
- Many users with many types of disabilities.
Related techniques:
- See techniques for checkpoint
7.3.
References:
- Refer to
Selection and Partial Selection of DOM Level 2 ([DOM2RANGE], section
2.2.2).
- For information about focus in the Motif environment (under X Windows),
refer to the OSF/Motif Style Guide [MOTIF].
7.2 Respect input configuration conventions. (P1)
- Ensure that default input
configurations do not interfere with
operating environment accessibility conventions.
User agent only.
Checkpoint 7.2
Note: In particular, default configurations should not
interfere with operating conventions for keyboard accessibility. See also checkpoint
11.5.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- The default configuration should not include
"Alt-F4",
"Control-Alt-Delete", or other combinations
that have reserved meanings in a given operating environment.
- Clearly document any default configurations that depart from operating
environment conventions.
Related techniques:
- Some reserved keyboard bindings are listed in the appendix on accessibility features of some operating
systems.
7.3 Operating environment conventions.
(P2)
- Follow
operating environment conventions that benefit accessibility. In
particular, follow conventions that benefit accessibility for
user interface design, keyboard
configuration, product installation, and
documentation.
User agent only.
Checkpoint 7.3
Note: Operating environment conventions that benefit
accessibility are those described in this document and in platform-specific
accessibility guidelines.
Notes and rationale:
- Much of the rationale behind the content requirements of User Agent
Accessibility Guidelines 1.0 also makes sense for the user agent user interface (e.g., allow the user
to turn off any blinking or moving user interface components).
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Follow operating environment conventions for loading assistive
technologies. See the appendix on loading assistive
technologies for DOM access for information about how an assistive
technology developer can load its software into a Java Virtual Machine.
- Inherit
operating environment settings related to accessibility (e.g., for
fonts, colors, natural
language preferences, input configurations, etc.).
- Ensure that any online services (e.g., automated update facilities,
download-and-install functionalities, sniff-and-fill forms, etc.) observe
relevant operating environment conventions concerning device independence and
accessibility (as well as the Web Content Accessibility Guidelines 1.0 [WCAG10]).
- Evaluate the conventional interface controls on the target platform against
any built-in operating environment accessibility functions (see the appendix on accessibility features of some operating
systems). Ensure that the user agent operates properly with all these
functions. Here is a sample of features to consider:
- Microsoft Windows offers an accessibility function called "High Contrast".
Standard window classes and controls automatically support this setting.
However, applications created with custom classes or controls work with the
"GetSysColor" API to ensure compatibility with High Contrast.
- Apple Macintosh offers an accessibility function called "Sticky Keys".
Sticky Keys operate with keys the operating environment recognizes as modifier
keys, and therefore a custom control should not attempt to define a new
modifier key.
- Maintain consistency in the user interface between versions of the
software. Consistency is less important than improved general accessibility and
usability when implementing new features. However, developers should make
changes conservatively to the layout of user interface
controls, the behavior of existing functionalities, and the default
keyboard configuration.
Related techniques:
- See techniques for checkpoint
6.4 and checkpoint
7.2.
References:
- Follow accessibility guidelines for specific platforms:
- "Macintosh Human Interface Guidelines" [APPLE-HI]
- "IBM Guidelines for Writing Accessible Applications Using 100% Pure Java"
[JAVA-ACCESS].
- "An Inter-client Exchange (ICE) Rendezvous Mechanism for
X Window System Clients" [ICE-RAP].
- "Information for Developers About Microsoft Active Accessibility" [MSAA].
- "The Inter-Client communication conventions manual" [ICCCM].
- "Lotus Notes accessibility guidelines" [NOTES-ACCESS].
- "Java accessibility guidelines and checklist"
[JAVA-CHECKLIST].
- "The Java Tutorial. Trail: Creating a GUI with JFC/Swing"
[JAVA-TUT].
- "The Microsoft Windows Guidelines for Accessible Software Design"
[MS-SOFTWARE].
- Follow general guidelines for producing accessible software:
- "Accessibility for applications designers" [MS-ENABLE].
- "Application Software Design Guidelines" [TRACE-REF]. Refer also to "EZ
ACCESS(tm) for electronic devices V 2.0 implementation guide" [TRACE-EZ]
from the Trace Research and Development Center.
- Articles and papers from Sun Microsystems about accessibility
[SUN-DESIGN].
- "EITAAC Desktop Software standards" [EITAAC].
- "Requirements for Accessible Software Design" [ED-DEPT].
- "Software Accessibility" [IBM-ACCESS].
- Towards Accessible Human-Computer Interaction" [SUN-HCI].
- "What is Accessible Software" [WHAT-IS].
- Accessibility guidelines for Unix and X Window applications
[XGUIDELINES].
7.4 Input configuration indications.
(P2)
- Follow
operating environment conventions to indicate the input
configuration.
User agent only.
Checkpoint 7.4
Note: For example, in some operating environments, when a
functionality may be triggered through a menu and through the keyboard, the
developer may design the menu entry so that the character of the activating key
is also shown. This checkpoint is an important special case of checkpoint 7.3. See also checkpoint
11.5.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Use
operating environment conventions to indicate the current
configuration (e.g., in menus, indicate what key strokes will activate the
functionality, underline single keys that will work in conjunction with a key
such as Alt, etc.) These are conventions used by the Sun Java
Foundations Classes [JAVA-TUT] and Microsoft
Foundations Classes for Windows.
- Ensure that information about changes to the input configuration is
available in a device-independent manner (e.g., through visual and audio cues,
and through text).
- If the current configuration changes locally (e.g., a search prompt opens,
changing the keyboard mapping for the duration of the prompt), alert the
user.
- Named configurations are easier to remember. This is especially important
for people with certain types of cognitive disabilities. For example, if the
invocation of a search prompt changes the input configuration, the user may
remember more easily which key strokes are meaningful in search mode if alerted
that there is a "Search Mode". Context-sensitive help (if available) should
reflect the change in mode, and a list of keybindings for the current mode
should be readily available to the user.
Related techniques:
- See input configuration
techniques.
Checkpoints
8.1 Implement accessibility features.
(P1)
- Implement the accessibility features of specifications (markup languages,
style sheet languages, metadata languages, graphics formats, etc.). For the
purposes of this checkpoint, an accessibility feature is either
- one identified as such, or
- one that allows the author to satisfy any requirement of the "Web Content
Accessibility Guidelines 1.0" [WCAG10].
Content only.
Checkpoint 8.1
Note: This checkpoint applies to both W3C-developed and
non-W3C specifications.
conformance and implementing specifications for more information.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Make obvious to users features that are known to benefit accessibility.
Make them easy to find in the user interface and in documentation.
- Some specifications include optional features (not required for conformance
to the specification). If an optional feature is likely to cause accessibility
problems, developers should either ensure that the user can turn off the
feature or they not implement the feature.
- Refer to the following list of accessibility features of HTML 4 [HTML4] (in
addition to those described in techniques for checkpoint 2.1):
References:
- Refer to the "Accessibility Features of CSS"
[CSS-ACCESS]. Note that CSS 2 includes properties for configuring
synthesized speech styles.
- Refer to the "Accessibility Features of SMIL"
[SMIL-ACCESS].
- Refer to the "Accessibility Features of SVG"
[SVG-ACCESS].
- For information about the Sun Microsystems Java Accessibility API in Java
JDK, refer to
[JAVAAPI].
- For information about captioning for the Synchronized Accessible Multimedia
Interchange (SAMI), refer to [SAMI].
8.2 Conform to specifications. (P2)
- Use and conform to
either
- W3C Recommendations when they are available and appropriate for a task,
or
- non-W3C specifications that enable the creation of content that conforms at
level A or better to the Web Content Accessibility Guidelines 1.0 [WCAG10].
- When a requirement of another specification contradicts a requirement of
the current document, the user agent may disregard the requirement of the other
specification and still satisfy this checkpoint.
Content only.
Checkpoint 8.2
Note: For instance, for markup, the user agent may conform to HTML 4 [HTML4], XHTML 1.0
[XHTML10], or XML 1.0 [XML]. For style sheets, the user
agent may conform to CSS ([CSS1], [CSS2]). For mathematics, the user
agent may conform to MathML 2.0 [MATHML20]. For synchronized
multimedia, the user agent may conform to SMIL 1.0 [SMIL]. A
specification is considered "available" if it is published (e.g., as a W3C
Recommendation) in time for integration into a user agent's development cycle.
The user agent is not required to satisfy this checkpoint for all implemented
specifications; see the section on
conformance and implementing specifications for more information.
Notes and rationale:
- The right to disregard only applies when the requirement of another
specification contradicts the requirements of the current document; no
exemption is granted if the other specification is consistent with or silent
about a requirement made by the current document.
- Conformance to W3C Recommendations is not a Priority 1 requirement because
user agents can (and should!) provide access for non-W3C specifications as
well.
- The requirement of this checkpoint is to conform to at least one
W3C Recommendation that is available and appropriate for a particular task, or
at least one non-W3C specification that allows the creation of content that
conforms to WCAG 1.0 [WCAG10]. For example, user agents
would satisfy this checkpoint by conforming to the Portable Network Graphics
1.0 specification
[PNG] for raster images. In addition, user agents may implement
other image formats such as JPEG, GIF, etc. Each specification defines what
conformance means for that specification.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- If more than one version or level of a specification is appropriate for a
particular task, user agents are encouraged to conform to the latest version.
However, developers should consider implementing the version that best supports
accessibility, even if this is not the latest version.
- For reasons of backward compatibility, user agents should continue to
implement deprecated features of specifications. Information about deprecated
language features is generally part of the language's specification.
References:
- The list of current W3C Recommendations and
other technical documents is available at
http://www.w3.org/TR/
.
- W3C make available validation services to promote the proper usage and
implementation of specifications. Refer to the:
- Information about PDF and accessibility is made available by Adobe [ADOBE].
Checkpoints
9.1 Provide content focus. (P1)
- Provide at least one content
focus for each viewport
(including frames) where enabled elements are part of the rendered
content.
- Allow the user to make the content focus of each viewport the
current focus.
Content only.
Checkpoint 9.1
Note: For example, when two frames of a frameset contain
enabled elements, allow the user to make the
content focus of either frame the current focus. Note that viewports
"owned" by
plug-ins that are part of a conformance
claim are also covered by this checkpoint.
Who benefits:
- Users who rely on the content
focus for interaction (e.g., for interaction with enabled elements
through the keyboard, or for assistive technologies that consider the current
focus a point of
regard). This includes some users with blindness, low vision, or a
physical disability.
Example techniques:
- None.
9.2 Provide user interface focus. (P1)
- Provide a user
interface focus.
User agent only. Checkpoint
9.2
Who benefits:
- Users who rely on the user
interface focus for interaction (e.g., for interaction with user
interface controls through the keyboard, or for assistive technologies that
consider the current focus a point of
regard). This includes some users with blindness, low vision, or a
physical disability.
Example techniques:
- Some
operating environments provide a means to move the
user interface focus among all open
windows using multiple input devices (e.g., keyboard and mouse). This technique
would suffice for switching among user agent viewports that are separate
windows.
9.3 Move content focus. (P1)
- Allow the user to move the content
focus to any enabled
element in the
viewport.
- If the author has not specified a navigation order, allow at least forward
sequential navigation to each element, in document order.
- The user agent may also include disabled elements in the navigation order.
Content only. Checkpoint
9.3
Note: In addition to forward sequential navigation, the
user agent should also allow reverse sequential navigation. This checkpoint is
an important special case of
checkpoint 9.9.
Who benefits:
- Users who rely on the focus for interaction (e.g., for interaction with
enabled elements through the keyboard, or for assistive technologies that
consider the focus a point of regard). This includes some users with blindness,
low vision, or a physical disability.
- Allow the user to move the content focus to each enabled element by
repeatedly pressing a single key. Many user agents today allow users to
navigate sequentially by repeating a key combination – for example, using
the Tab key for forward navigation and Shift-Tab for
reverse navigation. Because the Tab key is typically on one side of
the keyboard while arrow keys are located on the other, users should be allowed
to configure the user agent so that sequential navigation is possible with keys
that are physically closer to the arrow keys. See also checkpoint 11.3.
- Maintain a logical element navigation order. For instance, users may use
the keyboard to navigate among elements or element groups using the arrow keys
within a group of elements. One example of a group of elements is a set of
radio buttons. Users should be able to navigate to the group of buttons, then
be able to select each button in the group. Similarly, allow users to navigate
from table to table, but also among the cells within a given table (up, down,
left, right, etc.).
- Respect author-specified information about navigation order (e.g., the
"tabindex" attribute in HTML 4 [HTML4], section
17.11.1). Allow users to override the author-specified navigation order (e.g.,
by offering an alphabetized view of links or other orderings).
- The default sequential navigation order should respect the conventions of
the natural
language of the document. Thus, for most left-to-right languages,
the usual navigation order is top-to-bottom and left-to-right. For
right-to-left languages, the order would be top-to-bottom and
right-to-left.
- Implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). This allows users to modify content focus presentation with user style
sheets. Use them in conjunction with the
CSS 2 ':before' pseudo-elements ([CSS2], section 5.12.3) to clearly
indicate that something is a link (e.g., 'A:before { content : "LINK:"
}').
- In Java, a component is part of the sequential navigation order when added
to a panel and its
isFocusTraversable
method returns true. A
component can be removed from the navigation order by extending the component,
overloading this method, and returning false.
-
Doing more:
- Provide other sequential navigation mechanisms for particular element types
or semantic units, e.g., "Find the next table" or "Find the previous form." For
more information about sequential navigation of form
controls and form submission, see techniques for checkpoint 5.5.
- For graphical user agents (or any user agent offering a two-dimensional
display), navigation based not on document order but on layout may also benefit
the user. For example, allow the user to navigate up, down, left, and right to
the nearest rendered enabled link. This type of navigation may be particularly
useful when it is clear from the layout where the next navigation step will
take the user (e.g., grid layouts where it is clear what the next link to the
left or below will be).
- Excessive use of sequential navigation can reduce the usability of software
for both disabled and non-disabled users. Some useful types of direct
navigation include: navigation based on position (e.g., all links are numbered
by the user agent), navigation based on element content (e.g., the first letter
of text content), direct navigation to a table
cell by its row/column position, and searching (e.g., based on form element
text, associated labels, or form element names).
9.4 Restore history. (P1)
- For user agents that implement a viewport history mechanism, for each state
in a viewport's browsing history, maintain information about the point of
regard, content
focus, and
selection.
- When the user returns to any state in the viewport history, restore the
saved values for all of these state variables.
Content only.
Checkpoint 9.4
Note: For example, when the user uses the "back"
functionality, restore the four state variables.
Notes and rationale:
- This checkpoint only refers to a per-viewport history mechanism, not a
history mechanism that is common to all viewports (e.g., of visited Web
resources).
Who benefits:
- Users who may have difficulty re-orienting themselves during a browsing
session. This includes some users with a memory or cognitive disability, some
users with a physical disability, and some users who access content serially
and for whom repositioning will be time consuming (e.g., users with blindness
or low vision).
Example techniques:
- If the user agent allows the user to browse multimedia or
audio-only presentations, when the user leaves one presentation for
another, pause the presentation. When the user returns to a previous
presentation, allow the user to resume the presentation where it was paused
(i.e., return the point of
regard to the same place in space and time). Note:
This may be done for a presentation that is available "completely" but not for
a "live" stream or any part of a presentation that continues to run in the
background.
- Allow the user to configure whether leaving a viewport pauses a multimedia
presentation.
- If the user activates a broken link, leave the viewport where it is and
alert the user (e.g., in the status bar and with a
graphical or audio alert). Moving the viewport suggests that a link
is not broken, which may disorient the user.
- In JavaScript, the following may be used to change the Web resource in the
viewport, and navigate the history:
myWindow.home();
myWindow.forward();
myWindow.back();
myWindow.navigate("http://example.com/");
myWindow.history.back();
myWindow.history.forward();
myWindow.history.go( -2 );
location.href = "http://example.com/"
location.reload();
location.replace("http://example.com/");
Doing more:
- Restore the four state variables after the user refreshes the same
content.
References:
- Refer to the HTTP/1.1 specification for information about history
mechanisms ([RFC2616], section 13.13).
9.5 No events on focus change.
(P2)
- Allow
configuration so that moving the
content focus to or from an enabled element does not automatically activate any explicitly associated
event handlers.
Content only.
Checkpoint 9.5
Note: For instance, in this configuration for an HTML
document, do not activate any handlers for the 'onfocus
',
'onblur
', or 'onchange
' attributes. In this
configuration, user agents should still apply any stylistic changes (e.g., highlighting) that may occur when there is a
change in content
focus.
Notes and rationale:
- First-time users of a page may want access to link text before deciding
whether to follow (activate) the link. More experienced users of a page might
prefer to follow the link directly, without the intervening content focus
step.
Who benefits:
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques:
- Allow the following configurations:
- On invocation of the input binding, move focus to the associated enabled
element, but do not activate it.
- On invocation of the input binding, move focus to the associated enabled
element and prompt the user with information that will allow the user to decide
whether to activate the element (e.g., link title or text). Allow the user to
suppress future prompts for this particular input binding.
- On invocation of the input binding, move focus to the associated enabled
element and activate it.
9.6 Show event handlers. (P2)
- For the element with content
focus, make available the list of input device
event handlers explicitly associated with
the element.
Content only.
Checkpoint 9.6
Note: For example, allow the user to query the element with
content focus for the list of input device event handlers, or add them directly
to the serial navigation order. See checkpoint 1.2 for information about activation of event
handlers associated with the element with focus.
Who benefits:
- Users with blindness or some users with a physical disability, and anyone
without a pointing device.
Example techniques:
- For HTML content, the left mouse button is generally the only mouse button
that is used to activate event handlers associated with mouse clicks.
References:
- See checkpoint
1.2 for information about input device event handlers in HTML 4 [HTML4] and the
Document Object Model (DOM) Level 2 Events Specification
[DOM2EVENTS].
9.7 Move content focus optimally. (P2)
- Allow the user to move the content
focus to any enabled
element in the
viewport.
- If the author has not specified a navigation order, allow at least forward
and reverse sequential navigation to each element, in document order.
- The user agent must not include disabled elements in the navigation order.
Content only.
Checkpoint 9.7
Note: This checkpoint is a special case of checkpoint 9.3.
Who benefits:
- Users who rely on the focus for interaction (e.g., for interaction with
enabled elements through the keyboard, or for assistive technologies that
consider the focus a point of regard). This includes some users with blindness,
low vision, or a physical disability.
Related techniques:
- Apply the techniques of
checkpoint 9.3 to enabled elements only.
Doing more:
- Allow configuration so that disabled
elements are included in the navigation order. These elements cannot
be activated (as they are disabled), but their presence may lend continuity to
navigation.
9.8 Text search.
(P2)
- Allow the user to search within rendered text for a sequence of characters from
the
document character set.
- Allow the user to start a forward search (in document order) from any
selected or focused location in content.
- When there is a match do both of the following:
- move the viewport so that the matched text content is within it, and
- allow the user to search for the next instance of the text from the
location of the match.
- Alert the user when there is no match, when the search reaches the end of
content, and prior to any wrapping.
- Provide a case-insensitive search option for text in
scripts (i.e., writing systems) where case is significant.
Content only. Checkpoint
9.8
Note: If the user has not indicated a start position for
the search, the search should start from the beginning of content. Use
operating environments conventions for indicating the result of a
search (e.g., selection
or content
focus). A wrapping search is one that restarts automatically at the
beginning of content once the end of content has been reached.
Who benefits:
- Some users who access content serially (e.g., users with blindness or low
vision), some users with a cognitive disability (who may have difficulty
locating information among other information), and some users with a physical
disability (for whom navigation may be a significant effort).
Example techniques:
- Use the selection or focus to indicate found text. This will provide
assistive technologies with access to the text.
- Allow users to search all views (e.g., including views of the text
source).
- For extremely small viewports or extremely long matches, the entire matched
text content may not fit within the viewport. In this case, developers may move
the viewport to encompass the initial part of the matched content.
- The search string input method should follow
operating environment conventions (e.g., for international character
input).
- When the point of regard depends on time (e.g., for audio viewports), the
user needs to be able to search through content that will be available through
that viewport. This is analogous to content rendered graphically that is
reachable by scrolling.
- For frames, allow users to search for content in all frames, without having
to be in a particular frame.
- For multimedia presentations, allow users to search and examine
time-dependent media elements and links in a time-independent manner. For
example, present a static list of time-dependent links.
- Allow users to search the element content of form elements (where
applicable) and any label text.
- When searching a document, the user agent should not search text whose
properties prevent it from being visible (such as text that has
visibility="hidden"
), or equivalent text for elements with such
properties (such as "alt
" text for an image that has
visibility="hidden"
).
Doing more:
- If the number of matches is known, provide this information to orient the
user.
- It may be confusing to allow users to search for text content that is
not rendered (and thus that they have not viewed). If this type of search
is possible, alert the user of this particular search mode.
- Allow the following additional search functionalities:
- Allow the user to start a search from the beginning of the document rather
than from the current selection or focus.
- Provide distinct alerts for the situation where the user has searched
through all content or where the user has simply reached the end of the
document and needs to wrap to the beginning.
- Allow reverse search so the user doesn't not have to start he search from
the beginning of the document if the search goes too far.
- Allow the user to easily start a search from the beginning of the content
currently rendered in the viewport.
- Provide the option of searching through conditional content that is
associated with rendered content, and render the found conditional content
(e.g., by showing its relation to the rendered content).
References:
- For information about when case is significant in a
script, please refer to Section 4.1 of Unicode
[UNICODE].
9.9 Structured navigation. (P2)
- Allow the user to navigate efficiently to and among important structural
elements.
- Allow forward and backward sequential navigation to important structural
elements.
Content only.
Checkpoint 9.9
Note: This specification intentionally does not identify
which "important elements" must be navigable as this will vary according to
markup language. What constitutes "efficient navigation" may depend on a number
of factors as well, including the "shape" of content (e.g., serial navigation
of long lists is not efficient) and desired granularity (e.g., among tables,
then among the cells of a given table).
Who benefits:
- Users who access content serially, including users with blindness and some
users with a physical disability.
Notes and rationale:
- User agents should construct the navigation view with the goal of breaking
content into sensible pieces according to the author's design. In most cases,
user agents should not break down content into individual elements for
navigation; element-by-element navigation of the document object does not meet
the goal of facilitating navigation to important pieces of content. (The
navigation view may also be an expanding/contracting outline view; see checkpoint 10.5.) Instead,
user agents are expected to construct the navigation view based on markup.
Example techniques:
- In HTML 4
[HTML4], important elements include:
A
,
ADDRESS
, APPLET
, BUTTON
,
FIELDSET
, DD
, DIV
, DL
,
DT
, FORM
, FRAME
, H1-H6
,
IFRAME
, IMG
, INPUT
, LI
,
LINK
(if rendered), MAP
, OBJECT
,
OL
, OPTGROUP
, OPTION
, P
,
TABLE
, TEXTAREA
, and UL
. HTML also allows
authors to specify keyboard configurations ("accesskey", "tabindex"), which can
serve as hints about what the author considers important.
- Allow navigation based on commonly understood document models, even if they
do not adhere strictly to a Document Type Definition (DTD). For instance, in HTML,
although headings (H1-H6) are not containers, they may be treated as such for
the purpose of navigation. Note that they should be properly nested.
- Use the DOM ([DOM2CORE]) as the basis of
structured navigation (e.g., a postorder traversal). However, for well-known
markup languages such as HTML, structured navigation should take advantage of
the structure of the source tree and what is rendered.
- Follow
operating environment conventions for indicating navigation progress
(e.g.,
selection or
content focus).
- Allow the user to limit navigation to the cells of a table (notably left
and right within a row and up and down within a column). Navigation techniques
include keyboard navigation from cell to cell (e.g., using the arrow keys) and
page up/down scrolling. See the section on table
navigation.
- Alert the user when navigation has led to the beginning or end of a
structure (e.g., end of a list, end of a form, table row or column end, etc.).
See also checkpoint 1.3.
- For those languages with known (e.g., by specification, schema, metadata,
etc.) conventions for identifying important components, user agents should
construct the navigation tree from those components, allowing users to navigate
up and down the document tree, and forward and backward among siblings. As the
same time, allow users to shrink and expand portions of the document tree. For
instance, if a subtree consists of a long series of links, this will pose
problems for users with serial access to content. At any level in the document
tree (for forward and backward navigation of siblings), limit the number of
siblings to between five and ten. Break longer lists down into structured
pieces so that users can access content efficiently, decide whether they want
to explore it in detail, or skip it and move on.
- Tables and forms illustrate the utility of a recursive navigation
mechanism. The user should be able to navigate to tables, then change "scope"
and navigate within the cells of that table. Nested tables (a table within the
cell of another table) fit nicely within this scheme. However, the headers of a
nested table may provide important context for the cells of the same row(s) or
column(s) containing the nested table. The same ideas apply to forms: users
should be able to navigate to a form, then among the controls within that
form.
- Navigation and orientation go together. The user agent should allow the
user to navigate to a location in content, explore the context, navigate again,
etc. In particular, user agents should allow users to:
- Navigate to a piece of content that the author has identified as important
according to the markup language specification and conventional usage. In HTML,
for example, this includes headings, forms, tables, navigation mechanisms, and
lists.
- Navigate past that piece of content (i.e., avoid the details of that
component).
- Navigate into that piece of content (i.e., chose to view the details of
that component).
- Change the navigation view as they go, expanding and contracting portions
of content that they wish to examine or ignore. This will speed up navigation
and facilitate orientation at the same time.
- Provide context-sensitive navigation. For instance, when the user navigates
to a list or table, provide locally useful navigation mechanisms (e.g., within
a table, cell-by-cell navigation) using similar input commands.
- Allow users to skip author-specified navigation mechanisms such as
navigation bars. For instance, navigation bars at the top of each page at a Web
site may force users with screen readers or some physical disabilities to wade
through many links before reaching the important information on the page. User
agents may facilitate browsing for these users by allowing them to skip recognized navigation bars (e.g., through a
configuration option). Some techniques for this include:
- Providing a functionality to jump to the first non-link content.
- If the number of elements of a particular type is known, provide this
information to orient the user.
- In HTML, the MAP element may be used to mark up a navigation bar (even when
there is no associated image). Thus, users might ask that MAP elements not be
rendered in order to hide links inside the MAP element. User agents might allow
users to hide MAP elements selectively. For example, hide any MAP element with
a "
title
" attribute specified. Note: Starting in
HTML 4, the MAP element allows block content, not just AREA
elements.
- Allow depth-first as well as breadth-first navigation.
- Allow users to navigate synchronized multimedia presentations. See also checkpoint
4.5.
Doing more:
- Allow the user to navigate characters, words, sentences, paragraphs,
screenfuls, etc. according to conventions of the natural
language. This benefits users of speech-based user agents and has
been implemented by several screen readers, including Winvision
[WINVISION], Window-Eyes [WINDOWEYES], and JAWS for
Windows
[JFW].
References:
- The following is a summary of ideas provided by the National Information
Standards Organization with respect to Digital Talking Books
[TALKINGBOOKS]:
A talking book's "Navigation Control Center" (NCC) resembles a traditional
table of contents, but it is more. It contains links to all headings at all
levels in the book, links to all pages, and links to any items that the reader
has chosen not to have read. For example, the reader may have turned off the
automatic reading of footnotes. To allow the user to retrieve that information
efficiently, the reference to the footnote is placed in the NCC and the reader
can go to the reference, understand the context for the footnote, and then read
the footnote.
Once the reader is at a desired location and wishes to begin reading, the
navigation process changes. Of course, the reader may elect to read
sequentially, but often some navigation is required (e.g., frequently people
navigate forward or backward one word or character at a time). Moving from one
sentence or paragraph at a time is also needed. This type of local navigation
is different from the global navigation used to get to the location of what you
want to read. It is frequently desirable to move from one block element to the
next. For example, moving from a paragraph to the next block element which may
be a list, blockquote, or sidebar is the normally expected mechanism for local
navigation.
9.10
Configure important elements. (P3)
- Allow
configuration and control of
the set of important elements required by checkpoint 9.9 and checkpoint 10.5.
- Allow the user to include and exclude element types in the set of
elements.
Content only.
Checkpoint 9.10
Note: For example, allow the user to navigate only
paragraphs, or only headings and paragraphs, etc.
Who benefits:
- Users who access content serially, including users with blindness and some
users with a physical disability.
Example techniques:
- Allow the user to navigate HTML elements that share the
same "class" attribute.
- The CSS
'display' and
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively), allow the user to override the default settings in user style sheets.
Example.
The following CSS 2 style sheet will turn the display off of all
HTML elements inside the BODY element except heading elements:
<STYLE type="text/css">
BODY * { display: none }
H1, H2, H3, H4, H5, H6 { display: block }
</STYLE>
Another approach would be to use class selectors to identify those elements
to hide or display.
End example.
Doing more:
- Allow the user to navigate according to similar styles (which may be an
approximation for similar element types).
Checkpoints
10.1 Table orientation. (P1)
- Make available to the user the purpose of each table (e.g., as expressed in
a summary or table caption) and the relationships among the table cells and
headers.
Content only.
Checkpoint 10.1
Note: This checkpoint refers only to table information that
the user agent can recognize.
Depending on the table, some techniques may be more efficient than others for
conveying data relationships. For many tables, user agents rendering in two
dimensions may satisfy this checkpoint by rendering a table as a grid and by
ensuring that users can find headers associated with cells. However, for large
tables or small viewports, allowing the user to query cells for information
about related headers may improve access. This checkpoint is an important
special case of checkpoint
2.1.
Notes and rationale:
- The more complex the table, the more clues to table structure are needed.
Make available information summarizing table structure, including any table
head and foot rows, and possible row grouping into multiple table bodies,
column groups, header cells and how they relate to data cells, the grouping and
spanning of rows and columns that apply to qualify any cell value, cell
position information, table dimensions, etc.
Who benefits:
- Users for whom summaries are important (e.g., some users with a cognitive
or memory disability), and for whom two-dimensional relationships may be
difficult to process (e.g., users with blindness who have serial access to the
content, or some users with a cognitive disability). Renderings that provide
easy access to cell header information will also help some users with low
vision or a physical disability, for whom it may be time-consuming to scroll in
order to locate relevant headers.
Example techniques:
- Refer to the
THEAD, TBODY, and TFOOT elements of HTML 4 ([HTML4], section 11.2.3). These
elements may be "fixed" to the screen (or repeated on paper) with the 'fixed'
value of the
CSS2 'position' property ([CSS2], section 9.3.1). When these
elements are used by authors, users can scroll through data while retaining
headers and footers "in view".
- In HTML, beyond the TR, TH, and TD elements, the table attributes
"summary", "abbr", "headers", "scope", and "axis" provide information about
relationships among cells and headers. For more information, see the section on
table techniques.
- When rendering a table serially, allow the user to specify how cell header
information should be rendered before cell data information. Some possibilities
are illustrated by the
CSS2 'speak-header' property ([CSS2], section 17.7.1).
-
10.2 Highlight selection and focus.
(P1)
- Provide a mechanism for
highlighting the selection
and content
focus of each viewport.
- The highlight mechanism must not rely on color alone.
- Allow global
configuration of selection and focus highlight styles.
- For graphical viewports, if the highlight mechanism involves colors or text
decorations, allow the user to choose from among the full range of
colors or text decorations supported by the
operating environment.
Content only.
Checkpoint 10.2
Note: Examples of highlight mechanisms include foreground
and background color variations, underlining, distinctive voice pitches,
rectangular boxes, etc. Because the selection and focus change frequently, user
agents should not highlight them using mechanisms (e.g., font size variations)
that cause content to reflow as this may disorient the user. See also checkpoint
7.1.
Who benefits:
- Users with color deficiencies or blindness, for whom color will not be
useful. Also, some devices may not render colors (e.g., speech synthesizers,
black and white screens).
Example techniques:
- Inherit selection
and focus information from user's settings for the
operating environment.
- A highlighted selection or focus may span text with different background
colors, text foreground colors, font families, etc.
- For selection:
- For focus, implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). and
dynamic outlines and focus of CSS 2 ([CSS2], sections 5.11.3 and 18.4.1,
respectively).
Example.
The following rule will cause links with focus to appear with a blue
background and yellow text.
A:focus { background: blue; color: yellow }
The following rule will cause TEXTAREA
elements with focus to
appear with a particular focus outline:
TEXTAREA:focus { outline: thick black solid }
Doing more:
- Test the user agent to ensure that individuals who have low vision and use
screen magnification software are able to follow highlighted item(s).
10.3 Distinct default highlight
styles. (P1)
- Ensure that all of the default highlight
styles for the
selection, content
focus, enabled
elements, recently visited links, and fee
links
- do not rely on color alone, and
- differ from each other, and not by color alone.
- This checkpoint not apply to those highlight styles inherited from the
operating environment as default values, as long as the user can change the
styles in the operating environment.
Content only.
Checkpoint 10.3
Note: For instance, by default a graphical user agent may
present the selection using color and a dotted outline, the focus using a solid
outline, enabled elements as underlined in blue, recently visited links as
dotted underlined in purple, and fee links using a special icon or flag to draw
the user's attention.
Who benefits:
- For this checkpoint, and for others in this document, "color" includes
black, white, and greys.
- Users with color deficiencies or blindness, for whom color will not be
useful. Also, some devices may not render colors (e.g., speech synthesizers,
black and white screens).
Example techniques:
- If the user overrides the default styling for any one of these mechanisms,
the new styling may interfere with the others. Therefore, the user agent should
allow the user to configure them all at once or should alert the user to
potential conflicts when change are made. For instance, if the user configures
both the selection and focus highlighting to use colors, there may be a
conflict (especially if the colors are the same or similar).
- If default highlight styles are inherited from the operating environment,
document how to change them, or explain where to find this information in the
documentation for the operating environment.
10.4 Highlight special elements. (P2)
- Provide a mechanism for
highlighting all enabled
elements, recently visited links, and fee
links.
- Allow the user to configure the highlight styles. The highlight mechanism
must not rely on color alone.
- For graphical viewports, if the highlight mechanism involves colors, fonts,
or text
decorations, allow the user to choose from among the full range of
colors, fonts, or text decorations supported by the
operating environment.
- For an image map, the user agent must highlight the image map as a whole
and should allow configuration to highlight each enabled region.
Content only.
Checkpoint 10.4
Note: Examples of highlight mechanisms include foreground
and background color variations, font variations, underlining, distinctive
voice pitches, rectangular boxes, etc.
Notes and rationale:
- For example, most graphical user agents highlight all the links on a page
so that users know at a glance where to interact.
Who benefits:
- Users with color deficiencies or blindness, for whom color will not be
useful. Also, some devices may not render colors (e.g., speech synthesizers,
black and white screens). If different text styles are used, some users with
low vision may need to configure them.
Example techniques:
- Do not rely solely on fonts or colors to alert the user whether or not the
link has previously been followed. Allow the user to configure how information
will be presented (colors, sounds, status bar messages, some combination,
etc.).
- Use CSS2
[CSS2] to add style to these different classes of elements. In
particular, consider the
'text-decoration' property ([CSS2], section 16.3.1), aural
cascading style sheets, font properties, and color properties.
- For enabled elements, implement CSS2
attribute selectors to match elements with associated scripts ([CSS2], section
5.8).
- For fee links:
- The W3C specification "Common Markup for micropayment per-fee-links"
[MICROPAYMENT] describes how authors may mark up micropayment
information in an interoperable manner.
- Use conventional, accessible interface controls to present information
about fees and to prompt the user to confirm payment.
- For a link that has content
focus, allow the user to query the link for fee information (e.g.,
by activating a menu or key stroke).
-
Related techniques:
- For links, see the section on link
techniques, the visited links example in the section on generated content techniques, and techniques
for checkpoint 9.3.
Doing more:
- Test the user agent to ensure that individuals who have low vision and use
screen magnification software are able to follow highlighted item(s).
10.5
Outline view. (P2)
- Make available to the user an "outline" view of
content, composed of labels for important structural elements (e.g.,
heading text, table titles, form titles, etc.).
Content only.
Checkpoint 10.5
Note: This checkpoint is meant to provide the user with a
simplified view of content (e.g, a table of contents). What constitutes a label
is defined by each markup language specification. For example, in HTML, a
heading (H1
-H6
) is a label for the section that
follows it, a CAPTION
is a label for a table, the
"title
" attribute is a label for its element, etc. A label is not
required to be
text only. For important elements that do
not have associated labels, user agents may generate labels for the outline
view. For information about what constitutes the set of important structural
elements, please see the Note following checkpoint 9.9. By making the outline view navigable, it is
possible to satisfy this checkpoint and checkpoint 9.9 together: Allow users to navigate among the
important elements of the outline view, and to navigate from a position in the
outline view to the corresponding position in a full view of content. See also checkpoint
9.10.
Who benefits:
- The outline view is a type of summary view, and will benefit some users
with a memory or cognitive disability, as well as users for whom serial access
is time consuming (e.g., some users with blindness or a physical disability, or
some users with low vision). A navigable outline view will add further benefits
for these users.
Example techniques:
- For instance, in HTML, labels include the following:
- The
CAPTION
element is a label for TABLE
- The "
title
" attribute is a label for many elements.
- The
H1
-H6
elements are labels for sections that
follow
- The
LABEL
element is a label for form element
- The
LEGEND
element is a label for a set of form elements
- The
TH
element is a label for a row/column of table
cells.
- The
TITLE
element is a label for the document.
- Allow the user to expand or shrink portions of the outline view (configure
detail level) for faster access to important parts of content.
- Hide portions of content by using the CSS
'display' and
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively).
- Provide a structured view of form controls
(e.g., those grouped by
LEGEND
or OPTGROUP
in HTML)
along with their labels.
-
Related techniques:
- See structured navigation techniques for checkpoint 9.9.
Doing more:
- For documents that do not use structure properly, user agents may attempt
to create an outline based on the rendering of elements and heuristics about
what elements may indicate about document structure.
10.6 Provide link information. (P3)
- To help the user decide whether to traverse a link, make available the
following information about it:
- link element content,
- link title,
- whether the link is internal to the resource (e.g., the link is to a target
in the same Web page),
- whether the user has traversed the link recently,
- whether traversing it may involve a fee, and
- information about the type, size, and natural language of linked Web
resources.
- The user agent is not required to compute or make available information
that requires retrieval of linked Web
resources.
Content only. Checkpoint
10.6
Who benefits:
- Users for whom following a link may lead to loss of context upon return,
including some users with blindness and low vision, a memory or cognitive
disability, or a physical disability.
Example techniques:
- Some markup languages allow authors to provide hints about the nature of
linked content (e.g., in HTML 4 [HTML4], the "hreflang" and "type"
attributes on the A element). Specifications should indicate when this type of
information is a hint from the author and when these hints may be overridden by
another mechanism (e.g., by HTTP headers in the case of HTML). User agent
developers should make the author's hints available to the user (prior to
retrieving a resource), but should provide definitive information once
available.
- Links may be simple (e.g., HTML links) or more complex, such as those
defined by the XML Linking Language (XLink) [XLINK].
- The scope of "recently followed link" depends on the user agent. The user
agent may allow the user to configure this parameter, and should allow the user
to reset all links as "not followed recently".
- User agents should cache information determined as the result of retrieving
a Web resource and should make it available to the user. Refer to HTTP/1.1
caching mechanisms described in RFC 2616 [RFC2616], section 13.
- For a link that has content
focus, allow the user to query the link for information (e.g., by
activating a menu or key stroke).
- Do not mark all local links (to anchors in the same page) as visited when
the page has been visited.
Related techniques:
- See the section on link techniques.
Doing more:
- User agents may provide information about any input bindings associated
with a link. See
checkpoint 11.2.
References:
- User agents may use HTTP HEAD rather than GET for information about size,
language, etc. Refer to RFC 2616 [RFC2616], section 9.3
- For information about content size in HTTP/1.1, refer to RFC 2616 [RFC2616],
section 14.13. User agents are not expected to compute content size recursively
(i.e., by adding the sizes of resources referenced by URIs within another
resource).
- For information about content language in HTTP/1.1, refer to RFC 2616
[RFC2616], section 14.12.
- For information about content type in HTTP/1.1, refer to RFC 2616 [RFC2616],
section 14.17.
Checkpoints for the user interface
10.7 Highlight current viewport.
(P1)
- Provide a mechanism for
highlighting the viewport with the
current focus.
- For graphical viewports, the default highlight mechanism must not rely on
color alone.
- This default color requirement does not apply if the highlight mechanism is
inherited from the operating environment as the default and the user can change
it in the operating environment.
User agent only.
Checkpoint 10.7
Note: This includes highlighting and identifying frames.
This checkpoint is an important special case of checkpoint 1.1. See also
to checkpoint
checkpoint 7.1.
Who benefits:
- Users with color deficiencies or blindness, for whom color will not be
useful. Also, some devices may not render colors (e.g., speech synthesizers,
black and white screens).
Example techniques:
- Provide a setting that causes a window that is the viewport with the
current focus to be maximized automatically. For example, maximize the parent
window of the browser when launched, and maximize each child window
automatically when it receives focus.
Maximizing does not necessarily mean occupying the whole screen or parent
window; it means expanding the viewport so that users have to scroll
horizontally or vertically as little as possible.
- If the viewport with the current focus is a frame or the user does not want
windows to pop to the foreground, use colors, reverse videos, or other
graphical clues to indicate the viewport with the current focus.
- If the default highlight mechanism is inherited from the operating
environment, document how to change it, or explain where to find this
information in the documentation for the operating environment.
- For speech or braille output, use the frame or window title to identify the
viewport with the current focus.
- Use
operating environment conventions, for specifying selection and
content focus (e.g., schemes in Windows).
- Implement the
':hover', ':active', and ':focus' pseudo-classes of CSS 2 ([CSS2], section
5.11.3). This allows users to modify content focus rendering with user style sheets.
-
Related techniques:
- See the section on frame techniques.
10.8 Indicate rendering progress. (P3)
- Indicate the
viewport's position relative to rendered content (e.g., the proportion of an
audio or video clip that has been played, the proportion of a Web page that has
been viewed, etc.).
- For two-dimensional renderings, relative position includes both vertical
and horizontal positions.
Content only.
Checkpoint 10.8
Note: The user agent may calculate the relative position
according to content focus position, selection position, or viewport position,
depending on how the user has been browsing. The user agent may indicate the
proportion of content viewed in a number of ways, including as a percentage, as
a relative size in bytes, etc.
Notes and rationale:
- This checkpoint does not specify how to calculate the proportion in all
cases, and implementations may vary. For instance, suppose a user agent is to
render fifty audio clips one after the other. It may be costly to calculate the
proportion based on the total time required by all fifty clips (as this may
require the user agent to fetch all fifty in advance). Instead, the user agent
may represent the proportion as something like "2:43 remaining in the tenth
audio clip (of fifty)."
Who benefits:
- This type of context information benefits everyone, but is particularly
valuable to some users with serial access to content (e.g., users with
blindness) and to some users with a cognitive disability.
Example techniques:
- The proportion should be indicated using a relative value (where
applicable), otherwise as an absolute offset from some recognized
landmark.
- Provide a scrollbar for the viewport. Some specifications address scrolling
requirements or suggestions, such as for
the
THEAD
and TBODY
elements of HTML 4 ([HTML4], section
11.2.3) and the
'overflow' property of CSS 2 ([CSS2], section 11.1.1).
- Indicate the size of the document, so that users may decide whether to
download for offline viewing. For example, the playing time of an audio file
could be stated in terms of hours, minutes, and seconds. The size of a
primarily text-based Web page might be stated in both kilobytes and screens,
where a screen of information is calculated based on the current dimensions of
the viewport.
- Indicate the number of screens of information, based on the current
dimensions of the viewport (e.g., "screen 4 of 10").
- Use a variable pitch audio signal to indicate the viewport's different
positions.
- Provide markers for specific percentages through the document.
- Provide markers for positions relative to some position – a user
selected point, the bottom, the
H1
, etc.
- Put a marker on the scrollbar, or a highlight at the bottom of the page
while scrolling (so you can see what was the bottom before you started
scrolling).
- For images that render gradually (coarsely to finely), it is not necessary
to show percentages for each rendering pass.
Doing more:
- Allow users to configure what status information they want rendered. Useful
status information includes:
- Document proportions (numbers of lines, pages, width, etc.);
- Number of elements of a particular type (e.g., tables, forms, and
headings);
- Whether the viewport is at the beginning or end of the document;
- Size of document in bytes;
- The number of controls in a form and controls in a form element group
(e.g.,
FIELDSET
in HTML).
Checkpoints
11.1 Current user bindings. (P1)
- Provide information to the user about current user preferences for input
configurations.
User agent only.
Checkpoint 11.1
Note: To satisfy this checkpoint, the user agent may make
available binding information in a centralized fashion (e.g., a list of
bindings) or a distributed fashion (e.g., by listing keyboard shortcuts in user
interface menus).
Who benefits:
- Many users benefit from direct access to important user agent
functionalities (e.g., via a single key stroke or short voice command): users
with blindness (for whom the pointing device is not useful), users with poor
physical control (who might mistakenly repeat a key stroke), users who fatigue
easily (for whom the composition of key sequences is a significant effort),
users who cannot remember key combinations, and any user who wants to operate
the user agent efficiently.
Related techniques:
- See the input configuration
techniques.
11.2 Current author bindings.
(P2)
- Provide a centralized view of the current author-specified input
configuration bindings.
Content only.
Checkpoint 11.2
Note: For example, for HTML documents, provide a view of
keyboard bindings specified by the author through the "accesskey
"
attribute. The intent of this checkpoint is to centralize information about
author-specified bindings so that the user does not have to read the entire
content first to find out what bindings are available. The user agent may
satisfy this checkpoint by providing different views for different input
modalities (keyboard, pointing device, voice, etc.).
Who benefits:
- Refer to
checkpoint 11.2: some users with blindness, a physical disability, or a
memory or cognitive disability.
Example techniques:
- If the user agent offers a special view that lists author-specified
bindings, allow the user to navigate easily back and forth between the viewport
with the current focus and the list of bindings.
Related techniques:
- See input configuration
techniques.
Doing more:
- In addition to providing a centralized view of bindings, allow users to
find out about bindings in content. For example, highlight enabled elements
that have associated event handlers (e.g., by indicating bindings near the
element).
11.3 Override bindings. (P2)
- Allow the user to override
any binding that is part of the user agent default input
configuration.
- The user agent is not required to allow the user to override conventional
bindings for the
operating environment (e.g., for access to help).
User agent only.
Checkpoint 11.3
Note: The override requirement only applies to bindings for
the same input modality (e.g., the user must be able to override a keyboard
binding with another keyboard binding). See also checkpoint 11.5, checkpoint 11.7, and checkpoint 12.3.
Who benefits:
- Refer to
checkpoint 11.2: some users with blindness, a physical disability, or a
memory or cognitive disability.
Example techniques:
- Allow the user to override bindings at the level of the operating
environment.
Related techniques:
- See input configuration
techniques.
Doing more:
- Allow users to choose from among pre-packaged configurations, to override
some of the chosen configuration, and to save it as a
profile. Not only will the user save time configuring the user
agent, but this will reduce questions to technical support personnel.
- Allow users to restore easily the default input configuration.
- Allow users to create macros and bind them to key strokes or other input
methods.
- Test the default keyboard configuration for usability. Ask users with
different disabilities and combinations of disabilities to test
configurations.
11.4 Single key access. (P2)
- Allow the user to override
any binding in the user agent default keyboard configuration with a binding to
either a key plus modifier keys or to a single-key.
- For each functionality in the set required by checkpoint 11.5, allow the
user to configure
a single-key binding (i.e., one key press performs the task, with zero modifier
keys).
- If the number of physical keys on the keyboard is less than the number of
functionalities required by checkpoint 11.5, allow single-key bindings for as many of
those functionalities as possible.
- The single-key binding requirements may be satisfied with a "single-key
mode" (i.e., a mode where the current bindings are replaced by a set of
single-key bindings).
- The user agent is not required to allow the user to
override conventional bindings for the
operating environment (e.g., for access to help).
User agent only. Checkpoint
11.4
Note: In this checkpoint, "key" refers to a physical key of
the keyboard (rather than, say, a character of the document character set). Because single-key
access is so important to some users with physical disabilities, user agents
should ensure that (1) most keys of the physical keyboard may be configured for
single-key bindings, and (2) most functionalities of the user agent may be
configured for single-key bindings. This checkpoint does not require single
physical key bindings for character input, only for the activation of user
agent functionalities. For information about access to user agent functionality
through a keyboard API, see
checkpoint 6.6.
Notes and rationale:
- When using a physical keyboard, some users require single-key access,
others require that keys activated in combination be physically close together,
while others require that they be spaced physically far apart.
- In some modes of interaction (e.g., when the user is entering text), the
number of available single keys will be significantly reduced.
- A "single-key mode" allows user agents to "save" keys for other bindings by
default and still satisfy this checkpoint. However, even when a single-key mode
is offered, user agents should include as many required single-key bindings as
possible in the default keyboard configuration. The user should be able to
enter into a single-key mode by using a single-key.
Who benefits:
- Single-key access is particularly important to some users with a physical
disability, or a memory or cognitive disability (for simplicity's sake).
Example techniques:
- Offer a single-key mode where, once the user has entered into that mode
(e.g., by pressing a single key), most of the keys of the keyboard are
configurable for single-key operation of the user agent. Allow the user to exit
that mode by pressing a single key as well. For example, Opera [OPERA] includes a
mode in which users can access important user agent functionalities with single
strokes from the numeric keypad.
- Consider distance between keys and key alignment (e.g., "9/I/K", which
align almost vertically on many keyboards) in the default configuration. For
instance, if Enter is used to activate links, put other link
navigation commands near it (e.g., page up/down, arrow keys, etc. on many
keyboards). In configurations for users with reduced mobility, pair related
functionalities on the keyboard (e.g., left and right arrows for forward and
back navigation).
- Mouse Keys (available in some
operating environments) allow users to simulate the mouse through
the keyboard. They provide a usable command structure without interfering with
the user interface for users who do not require keyboard-only and single-key
access.
Doing more:
- Allow users to accomplish tasks through repeated key strokes (e.g.,
sequential navigation) since this means less physical repositioning for all
users. However, repeated key strokes may not be efficient for some tasks. For
instance, do not require the user to position the pointing device by pressing
the "down arrow" key repeatedly.
- So that users do not mistakenly activate certain functionalities, make
certain combinations "more difficult" to invoke (e.g., users are not likely to
press Control-Alt-Delete accidentally).
11.5
Default binding requirements. (P2)
- Ensure that the user agent default input configuration includes bindings for the
following functionalities required by other checkpoints in this document:
- move focus to next enabled
element, and move focus to previous enabled element;
- activate focused link;
- search for text;
- search again for same text;
- increase size of rendered
text, and decrease size of rendered text;
- increase global volume, and decrease global volume;
- stop, pause, resume, fast advance, and fast reverse selected audio and animations (including video and animated
images).
- If the user agent supports
the following functionalities, the default input configuration must also
include bindings for them:
- next history state (forward), and previous history state (back);
- enter URI for new resource;
- add to favorites (i.e., bookmarked resources);
- view favorites;
- stop loading resource;
- reload resource;
- refresh rendering;
- forward one viewport, and back one viewport;
- next line, and previous line.
User agent only.
Checkpoint 11.5
Note: This checkpoint does not make any requirements about
the ease of use of default input configurations, though clearly the default
configuration should include single-key bindings and allow easy operation. Ease
of use is ensured by the configuration requirements of checkpoint 11.3.
Who benefits:
- Refer to
checkpoint 11.2: some users with blindness, a physical disability, or a
memory or cognitive disability.
Example techniques:
- Input configurations should allow quick and direct navigation that does not
rely on graphical
output. Do not require the user to navigate through a graphical user interface
as the only way to activate a functionality.
Related techniques:
- See the techniques for checkpoint 7.4
Doing more:
- Provide different input configuration profiles
(e.g., one keyboard profile with key combinations close together and another
with key combinations far apart).
- Offer a mode that makes the input configuration compatible with other
versions of the software (or with other software).
- Provide convenient bindings for controlling the user interface, such as
showing, hiding, moving, and resizing graphical
viewports.
- Allow the user to configure how much the viewport should move when
scrolling the viewport backward or forward through content (e.g., for a
graphical viewport, "page down" causes the viewport to move half the height of
the viewport, or the full height, or twice the height, etc.).
11.6 User profiles. (P2)
- For the configuration requirements of this document, allow the user to save
user preferences in at least one user
profile.
- Allow the user to choose from among available default profiles, profiles
created by the same user, and no profile (i.e., the user agent default
settings).
User agent only. Checkpoint
11.6
Note: The configuration requirements of the checkpoints in
this document involve user preferences for styles, presentation rates, input
configurations, navigation, viewport behavior, and user agent
prompts and alerts.
Notes and rationale:
- The user agent is only expected to allow the user to choose from profiles
created by the same user, not profiles created by other users.
Who benefits:
- Refer to
checkpoint 11.2: some users with blindness, a physical disability, or a
memory or cognitive disability.
Example techniques:
- Follow applicable
operating environment conventions for input configuration profiles.
- Allow users to choose a different profile, to switch rapidly between
profiles, and to return to the default input configuration.
- If the user can edit the profile by hand, the user agent documentation
should explain the profile format.
11.7 Configure tool bars. (P3)
- For graphical user interfaces, allow the user to
configure the position of controls on tool bars of the user
agent user interface, to add or remove controls for the user
interface from a predefined set, and to restore the default user
interface.
User agent only.
Checkpoint 11.7
Note: This checkpoint is a special case of checkpoint 11.3.
Who benefits:
- Users for whom serial navigation may be difficult (e.g,. some users with
blindness or a physical disability). Some users with a memory or cognitive
disability (who may have difficulty remembering where and how to access user
agent functionalities).
Example techniques:
- Use conventional
operating environment controls for allowing configuration of font
sizes, speech rates, and other style parameters.
- Allow the user to show and hide controls. This benefits users with
cognitive disabilities and users who navigate user interface controls
sequentially.
- Allow the user to choose icons and/or text.
- Allow the user to change the grouping of icons and the order of menu
entries (e.g., for faster access to frequently used controls).
- Allow multiple icon sizes (big, small, other sizes). Ensure that these
values are applied consistently across the user interface.
- Allow the user to change the position of control bars, icons, etc. Do not
rely solely on drag-and-drop for reordering tool bar. Allow the user to
configure the user
agent user interface in a device-independent manner (e.g., through a
text-based
profile).
Checkpoints
12.1 Accessible documentation. (P1)
- Ensure that at least one version of the user agent
documentation conforms to at least Level
Double-A of the Web Content Accessibility Guidelines 1.0
[WCAG10].
User agent only.
Checkpoint 12.1
Notes and rationale:
- User agents may provide documentation in many formats, but at least one
must conform to at least Level Double-A of the Web Content Accessibility
Guidelines 1.0
[WCAG10].
- Remember to keep documentation accessible as the user agent evolves (e.g.,
when bug fixes are published, etc.).
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Distribute accessible documentation over the Web, on CD-ROM, or by
telephone. Alternative hardcopy formats may also benefit some users.
- For example, for conformance to the Web Content Accessibility Guidelines
1.0
[WCAG10]:
- Provide text
equivalents of all non-text
content (e.g., graphics, audio-only presentations, etc.);
- Provide extended descriptions of screen-shots, flow charts, etc.;
- Provide a text
equivalent for audio user agent tutorials. Tutorials that use speech
to guide a user through the operation of the user agent should also be
available at the same time as graphical
representations.
- Use clear and consistent navigation and search mechanisms;
- Use the
NOFRAMES
element when the support/documentation is
presented in a FRAMESET
;
- See also checkpoint
12.3.
- Describe the user interface with device-independent terms. For example, use
"select" instead of "click on".
- Provide documentation in small chunks (for rapid downloads) and also as a
single source (for easy download and/or printing). A single source might be a
single HTML file or a compressed archive of several
HTML documents and included images.
- Ensure that run-time help and any Web-based help or support information is
accessible and may be operated with a single, well-documented, input command
(e.g., key stroke). Use
operating environment conventions for input configurations related
to run-time help.
- Ensure that user agent identification codes are accessible to users so they
may install their software. Codes printed on software packaging may not be
accessible to people with visual disabilities.
Doing more:
- Provide accessible documentation for all audiences: end users, developers,
etc. For instance, developers with disabilities may wish to add accessibility
features to the user agent, and so require information on available APIs and other implementation details.
- Provide documentation in alternative formats such as braille (refer to
"Braille Formats: Principles of Print to Braille Transcription 1997"
[BRAILLEFORMATS]), large print, or audio tape. Agencies such as
Recording for the Blind and Dyslexic [RFBD] and the National Braille Press
[NBP] can
create alternative formats.
12.2 Document accessibility features.
(P1)
-
Document all user agent features that benefit accessibility.
- For the purposes of this checkpoint, a user agent feature that benefits
accessibility is one implemented to satisfy the requirements of this document
(including the requirements of checkpoints 8.1 and 7.3).
User agent only.
Checkpoint 12.2
Note: The help system should include discussion of user
agent features that benefit accessibility. The documentation of accessibility
features should be integrated into the documentation as a whole; see also checkpoint 12.5.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Document any features that affect accessibility and that depart from system
conventions.
- Provide a sensible index to accessibility features. For instance, users
should be able to find "How to turn off blinking text" in the documentation
(and the user interface). The user agent may support this feature by turning
off scripts, but users should not have to guess (or know) that turning off
scripts will turn off blinking text.
- Document configurable features in addition to defaults for those
features.
- Document the features implemented to conform with these guidelines.
- Include references to accessibility features in both the table of contents
and index of the documentation.
- If configuration files are used to satisfy the requirements of this
document, the documentation should explain the configuration file formats.
- In developer documentation, document the APIs that are required by this
document. Please see the requirements of guideline 6.
12.3 Document default bindings.
(P1)
-
Document the default user agent input configuration (e.g., the default keyboard
bindings).
User agent only.
Checkpoint 12.3
Note: If the default input configuration is inconsistent
with conventions of the operating environment, the documentation should alert
the user.
Notes and rationale:
- Documentation of keyboard accessibility is particularly important to users
with visual disabilities and some types of physical disabilities. Without this
documentation, a user with a disability (or multiple disabilities) may not
think that a particular task can be performed. Or the user may try to use a
much less efficient technique to perform a task, such as using a mouse, or
using an assistive technology's mouse emulation through key strokes.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- If the user agent inherits default values (e.g,. for the input
configuration, for highlight styles, etc.) from the operating environment,
document how to modify them in the operating environment, or explain where to
find this information in the documentation for the operating environment.
References:
- As an example of online documentation of keyboard support, refer to the Mozilla
Keyboard Planning FAQ and Cross Reference for the Mozilla browser
[MOZILLA].
12.4 Document changes. (P2)
-
Document changes from the previous version of the user agent to
accessibility features, including accessibility features of the user
interface.
User agent only.
Checkpoint 12.4
Note: Accessibility features are those defined in checkpoint 12.2.
Who benefits:
- Many users with many types of disabilities.
Notes and rationale:
- In particular, document changes to the user interface.
Example techniques:
- Either describe the changes that affect accessibility in the section of the
documentation dedicated to accessibility features (see checkpoint 12.5) or link
to the changes from the dedicated section.
- Provide a text description of changes (e.g., in a README file).
12.5 Dedicated section on accessibility.
(P2)
- In a dedicated section of the
documentation, describe all features of the user agent that benefit
accessibility.
User agent only.
Checkpoint 12.5
Note: The features that benefit accessibility are those
defined in checkpoint
12.2. This is a more specific requirement than checkpoint 12.2.
Who benefits:
- Many users with many types of disabilities.
Example techniques:
- Integrate information about accessibility features throughout the
documentation. The dedicated section on accessibility should provide access to
the documentation as a whole rather than standing alone as an independent
section. For instance, in a hypertext-based help system, the section on
accessibility may link to pertinent topics elsewhere in the documentation.
- Ensure that the section on accessibility features is easy to find.
This section presents general accessibility techniques that may apply to
more than one checkpoint.
User agents need to ensure that users have access to
content, either
rendered through the user interface or made available to assistive
technologies through an API. While providing serial access to a stream
of content would satisfy this requirement, this would be analogous to offering
recorded music on a cassette: other technologies exist (e.g., CD-ROMs) that
allow direct access to music. It is just as important for user agents to allow
users to access Web content efficiently, whether the content is being rendered
as a two-dimensional graphical
layout, an audio stream, or a line-by-line braille stream. Providing efficient
access to content involves:
- Preserving structure when rendering;
- Allowing the user to select specific content and query its structure or
context (what am I examining?);
- Using and generating metadata to provide context (where am I?).
These topics are addressed below.
When used properly, markup languages structure content in ways that allow
user agents to communicate that structure across different renderings. A table
describes relationships among cells and headers. Graphically, user agents
generally render tables as a two-dimensional grid. However, serial renderings
(e.g., speech and braille) also need to make those relationships apparent,
otherwise users may not understand the purpose of the table and the
relationships among its cells (see the section on
table techniques). User agents need to render content in ways that allow
users to understand the underlying document structure, which may consist of
headings, lists, tables, synchronized multimedia, link relationships, etc.
Providing alternative renderings (e.g., an outline view) will also help users
understand document structure.
Note: Even though the structure of a language like HTML may
be defined by a Document Type Definition (DTD), user agents
may convey structure according to a "more intelligent" document model when that
model is well-known. For instance, in the HTML DTD, heading
elements (H1 - H6) do not nest, but presenting the document as nested headings
may convey the document's structure more effectively than as a flat list of
headers.
The guidelines emphasize the importance of navigation as a way to provide
efficient access to content. Navigation allows users to access content more
efficiently and, when used in conjunction with
selection and focus
mechanisms, allows users to query content for metadata. For instance, blind
users often navigate a document by skipping from link to link, deciding whether
to follow each link based on metadata about the link. User agents can help them
decide whether to follow a link by allowing them to query each focused link for
the link text, title information, information about whether the link has been
visited, whether the link involves a fee, etc. While much of this information
may be rendered, the information has to also be available to assistive
technologies.
For example, the Amaya browser/editor [AMAYA] makes available all attributes and their values to the user through
a context menu. The user selects an element and
opens an attribute menu that shows which attributes are available for the
element and which have been assigned values. The user may read or write values
to attributes (since Amaya is an editor as well as a browser). Information
about attributes is also available through Amaya's structured view, which
renders the document tree as structured text.
The selection may be widened (moved to the nearest node one level up the
document tree) by pressing the Escape key; this is a form of
structured navigation based on the underlying document
object model.
Users may want to select content based on structure alone (as offered by
Amaya) but also based on how the content has been rendered. For instance, most
user agents allow users to select ranges of rendered text that may cross
"element boundaries".
Authors and user agents provide context to users through content, structure,
navigation mechanisms, and query mechanisms. Titles, dimensions, dates,
relationships, the number of elements, and other metadata all help orient the
user, particularly when available as text. For instance, user agents can help
orient users by allowing them to request that document headings and lists be
numbered. See also the section on table
techniques, which explains how user agents can offer table navigation and
the ability to query a table cell for information about the cell's row and
column position, associated header information, etc.
- User agents can use style sheet languages such as CSS 2 [CSS2] and XSLT
[XSLT] to
generate context information (see techniques for
generated content).
- For information about elements and attributes that convey metadata in HTML,
refer to the index of elements and attributes in "Techniques for Web Content
Accessibility Guidelines 1.0" [WCAG10-TECHS].
- For information about elements and attributes that convey metadata in SMIL,
refer to the index of attributes in the W3C Note "Accessibility Features of
SMIL"
[SMIL-ACCESS].
- Describe a selected element's position within larger structures (e.g.,
numerical or relative position in a document, table, list, etc.). For example:
tenth link of fifty links; document heading 3.4; list one of two, item 4.5;
third table, three rows and four columns; current cell in third row, fourth
column; etc. Allow users to get this information on demand (e.g., through a
keyboard shortcut). Provide this information on the status line on demand from
the user.
To ensure accessibility, users need to be able to configure the style of rendered
content and the user interface. Author-specified styles, while
important, may make content inaccessible to some users. User agents need to
allow users to increase the size of rendered text (e.g.,
with a zoom mechanism or font size control), to change colors and color
combinations, to slow down multimedia presentations, etc.
To give authors design flexibility and allow users to control important
aspects of content style, user agents should implement CSS ([CSS1], [CSS2]) and allow
users to create and apply user style
sheets. CSS includes mechanisms for tailoring rendering for a
particular output medium, including audio, braille, screen, and print.
- User agents should implement the
cascade order of CSS 2 ([CSS2], section 6.4.1) not CSS 1. In
CSS 2, user style sheets with
"!important" declarations (section 6.4.2) take precedence over
author styles. Refer also to Web
Content Accessibility Guidelines 1.0 checkpoint 3.3 [WCAG10].
- CSS-enabled user agents should consider as part of the cascade the markup
used for style, giving it a lower weight than actual style sheets. This allows
authors to specify style through markup for older user agents and to use more
powerful style sheets for CSS-enabled user agents. Refer to the section on the
precedence of non-CSS presentational hints in CSS 2 ([CSS2], section
6.4.4).
- To hide the CSS syntax from the user, user agents may implement user style
sheets through the user
agent user interface. User agents can generate a user style sheet
from user preferences or behave as though it did. Amaya [AMAYA] provides a
GUI-based interface to
create and apply internal style sheets. The same technique may be used to
control a user style sheet.
- In JavaScript, the following may be used to change style information:
document.all.myElement style.color = "red";
User agents make links accessible by providing navigation to links, helping
users decide whether to follow them, and allowing interaction in a
device-independent manner. Link techniques include the following:
- See sequential navigation techniques for
information about navigating to links.
- Provide a link view that lists all links in the document. Allow the user to
configure how the links are sorted (e.g., by document order, sequential
navigation order, alphabetical order, visited or unvisited or both, internal or
external or both, etc.).
- Help the user remember links by including metadata in the link view. For
example, identify a selected link as "Link X of Y", where "Y" is the total
number of links. Lynx
[LYNX] numbers each link and provides information about the relative
position in the document. Position is relative to the current page and the
number of the current page out of all pages. Each page usually has 24
lines.
- Allow the user to configure how much information about a link to present in
the content view (when a link receives focus). For
instance, allow the user to choose between "Display links using hyperlink text"
or "Display links by title (if present)", with an option to toggle between the
two views. For a link without a title, use the link text.
- For example, here is an algorithm for ensuring that an HTML link that has
image content has associated text.
- If the author has specified conditional content (that is not
empty) for the image (e.g., "alt" in
HTML), use that as the link text;
- Otherwise, use the link title if available;
- [Repair] Otherwise, use title information of the designated
Web resource (e.g., the TITLE element of
HTML for links to HTML documents).
- [Repair] Otherwise, render part of the filename or URI of the designated
Web resource.
- [Repair] Otherwise, insert a generic text
placeholder (e.g., [LINK]) in place of the image (if configured to
do so).
- For an image in link content, ensure that the user has access to the link
and any long description associated with the
image.
User agents can make lists accessible by ensuring that list structure
– and in particular, embedded list structure – is available through
navigation and rendering.
- Allow users to turn on "contextual" rendering of lists (even for unordered
"bullet" lists). Use compound numbers (or letters, numbers, etc.) to introduce
each list item (e.g., "1, 1.1, 1.2, 1.2.1, 1.3, 2, 2.1"). This provides more
context and does not rely on the information conveyed by a graphical rendering,
as in:
1.
1.
2.
1.
3.
2.
1.
which might be serialized for speech or braille as "1, 1, 2, 1, 2, 3, 2,
1".
- Specify list numbering styles in CSS. Refer to the section generated
content, automatic numbering, and lists in CSS ([CSS2], section 12).
Example.
The following CSS 2 style sheet (taken from CSS
2, section 12.5) shows how to specify compound numbers for nested lists
created with either UL or OL elements. Items are numbered as "1", "1.1",
"1.1.1", etc.
<STYLE type="text/css">
UL, OL { counter-reset: item }
LI { display: block }
LI:before { content: counters(item, "."); counter-increment: item }
</STYLE>
End example.
The HTML TABLE element was designed to represent
relationships among data ("data" tables). Even when authored well and used
according to specification, tables may pose problems for users with
disabilities for a number of reasons:
- Users who access a table serially (e.g., as speech or braille) may have
difficulty grasping the relationships among cells, especially for large and
complex tables.
- Users with cognitive disabilities may have trouble grasping or remembering
relationships between cells and headers, especially for large and complex
tables.
- Users of screen magnifiers or with physical disabilities may have
difficulties navigating to the desired cells of a table.
For these situations, user agents may assist these users by providing table
navigation mechanisms and supplying context that is present in a
two-dimensional rendering (e.g., the cells surrounding a given cell).
To complicate matters, many authors use tables to lay out Web content
("layout" tables). Not only are table structures used to lay out objects on the
screen, table elements such as TH (table header) in HTML are used to font
styling rather than to indicate a true table header. These practices make it
difficult for assistive technologies to rely on markup to convey document
structure. Consequently, assistive technologies often resort to interpreting
the rendered
content, even though the rendered content has "lost" information
encoded in the markup. For instance, when an assistive technology "reads" a
table from its graphical rendering, the contents of multiline cells may become
intermingled. For example, consider the following table:
This is the top left cell This is the top right cell
of the table. of the table.
This is the bottom left This is the bottom right
cell of the table. cell of the table.
Screen readers that read rendered content line by line would read the table
cells incorrectly as "This is the top left cell This is the top right cell". So
that assistive technologies are not required to gather incomplete information
from renderings, these guidelines require that user agents provide access to content through an
API (see checkpoint 6.3).
The following sections discuss techniques for providing improved access to
tables.
Users of screen readers or other serial access devices cannot gather
information "at a glance" about a two-dimensional table. User agents can make
tables more accessible by providing the user with table metadata such as the
following:
- The table caption (the
CAPTION
element in HTML) or summary
information (the "summary
" attribute in HTML).
- The number of column groups and columns. Note that the number of columns
may change according to the row. Also, some parts of a table may have two
dimensions, others three, others four, etc. Project dimensionality higher than
two onto two when rendering information.
- The number of row groups and rows, in particular information about table
headers and footers.
- Which rows contain header information (whether at the top or bottom of the
table).
- Which columns contain header information (whether at the left or right of
the table).
- Whether there are subheads.
- How many rows or columns a header spans.
When navigating, quick access to table metadata will allow users to decide
whether to navigate within the table or skip over it. Other techniques:
- Allow users to query table summary information from inside a cell.
- Allow the user to choose different levels of detail for the summary (e.g.,
brief table summary and a more detailed summary).
- Allow the user to configure navigation so that table metadata is not
(re-)rendered each time the user enters the table.
A linear rendering of tables – cells presented one at a time, row by
row or column by column – may be useful, but generally only for simple
tables. For more complex tables, user agents need to convey more information
about relationships among cells and their headers. A linear rendering of a
table may be useful as an equivalent for a multi-dimensional table.
Note: The following techniques apply to columns as well as
rows. The elements listed in this section are HTML
4.01 table elements ([HTML4], section 11).
- Provide access to one row at a time, beginning with any column header. If a
header is associated with more than one row, offer that header for each row
concerned.
- Render cells with their associated headers. Allow the user to configure how
often headers are rendered (e.g., by implementing the
'
speak-header
' property in CSS 2 [CSS2], section 17.7.1). Note also
that
the "abbr
" attribute in HTML 4 specifies
abbreviated headers for speech and other rendering ([HTML4], section 11.2.6). See also
information about cell headers later in this
section.
- Provide access to cell content as marked up in the document source.
- Refer to techniques for authoring accessible tables in "Techniques for Web
Content Accessibility Guidelines 1.0" [WCAG10-TECHS].
The most important aspect of rendering a table cell is that the cell's
contents be rendered faithfully and be identifiable as the contents of a single
cell. However, user agents may provide additional information to help orient
the user:
- Render the row and column position of the cell in the table.
- Indicate how many rows and columns a cell spans.
- Since the contents of a cell in a data table may only be comprehensible in
context (i.e., with associated header information, row/column position,
neighboring cell information etc.), allow users to navigate to cells and query
them for this information.
- For HTML tables, refer to the
section on associating header information with data cells of
HTML 4 ([HTML4], section 11.4.1).
- In a table with a leading row and column of
TH
cells, the
interpretation of the corner cell as an
empty TD
or TH
should not contribute to
the set of headings for cells in that row and column.
- For nested tables, render information about the level of nesting.
- Since a cell may belong to N different dimensions in a multi-dimensional
table, provide information about headers from each dimension.
2.5.4
Properly constructed data tables distinguish header cells from data cells.
How headers are associated with table cells depends on the markup language. The
following algorithm is based on the
HTML 4.01 algorithm to calculate header information ([HTML4], section
11.4.3). For the sake of brevity, it assumes a left-to-right ordering, but will
work for right-to-left tables as well (refer to the
"dir
" attribute of HTML 4 [HTML4], section
8.2). For a given cell:
- Search left from the cell's position to find row header (
TH
)
cells. Then search upwards from the cell's position to find column header
cells. The search in a given direction stops when the edge of the table is
reached or when a data cell is found after a header cell. If no headers are
found in either direction (left or up), search in the other directions (right
or down).
- Allow the user to configure where the header text comes from. For example,
in HTML 4, either the header cell element's content or the value of the
"
abbr
" attribute value ([HTML4], section 11.2.6).
- Insert row headers into the list in the (left-to-right) order they appear
in the table. Include values implicitly resulting from header cells in prior
rows with
rowspan="R"
, sufficient to extend into the current
row.
- Insert column headers after row headers, in the (top-to-bottom) order they
appear in the table. Include values implicitly resulting from header cells in
other columns with
colspan="C"
, sufficient to extend into the
current column containing the TD
cell.
- If a header cell has a value for the "headers" attribute, then insert it
into the list and stop the search for the current direction.
- Treat cells with a value for the "axis" attribute as header cells.
- Be sure to take into account header cells that span several rows or
columns.
2.5.5
Not all data tables include proper header markup, which the user agent may
be able to detect. Some repair strategies for finding header information
include the following:
- Consider that the top or bottom row contains header information.
- Consider that the leftmost or rightmost column in a column group contains
header information.
- If cells in an edge row or column span more than one row or column,
consider the following row or column to contain header information as
well.
- When trying to guess table structure, present several solutions to the
user.
Other repair issues to consider:
- Consider
TH
cells on both the left and right of the
table.
- For
TH
cells with "rowspan" set: consider the content of those
TH
cells for each of the N-1 rows below the one containing that
TH
content.
- An internal
TH
surrounded by TD
s makes it
difficult to know whether the header applies to cells to its left or right in
the same row (or in both directions) or cells above or below it in the same
column (or in both directions).
- Finding column header cells assumes they are all above the
TD
cell to which they apply.
- A
TH
element with "colspan
" set needs to be
included in the list of TH
s for the N-1 columns to its
right.
To permit efficient access to tables, user agents should allow users to
navigate to tables and within tables, to select individual cells, and to query
them for information about the cell and the table as a whole.
- Allow users to navigate to a table, down to one of its cells, and back up
to the table level. This should work recursively for nested tables.
- Allow users to navigate to a cell by its row and column position.
- Allow users to navigate to all cells under a given header.
- Allow users to navigate row by row or column by column.
- Allow users to navigate to the cells around the current cell.
- Allow users to navigate to the first or last cell of a row, column, or the
table.
- Allow users to navigate from a cell directly to its related headers (if
it's possible to navigate to the headers).
- Allow the user to search for text content
within a table (i.e., without searching outside of the table). Allow the user
to search for text within specific rows or columns, row groups or column
groups, or limited by associated headers.
- Alert the user when the navigation reaches a table edge and when a cell
contains another table.
- Allow relative and direct navigation. For example, entering "-3, 20" might
mean "left three cells, up 20 cells").
- Allow navigation of table headers or footers only.
- Consider the issues raised by navigation to or from a cell that spans more
than one row or column.
- For examples of table navigation, refer to the table navigation script from
the Trace Research Center [TABLENAV].
One way to make an image map accessible to some users (e.g., users with
blindness) is to render the links it contains as text links. This allows
assistive technologies to render the links a speech or braille, and benefits
users with slow access to the Web and users of small Web devices that do not
support images but can support hypertext. User agents may allow users to toggle
back and forth between a graphical mode for image maps and a text mode.
To construct a text version of an
image map in HTML:
- If the content of the
MAP element includes links, use them.
- Otherwise, for each AREA in the map, if (not
empty)
conditional text content is available (the "alt" attribute), use it
as the content of a generated link.
- When the author has specified empty conditional text content
("
alt=''
"), do not render the link.
- When the author has specified no text equivalent (no "alt"), render "Map
area" (or similar) followed by part of the URI of the link.
Furthermore, user agents that render a text image map instead of an image
may preface the text image map with inline metadata such as:
- a string that announces the image map (e.g., "Start map")
- any conditional text content associated with the image (e.g., "alt" for
IMG).
- the number of links in the map.
Allow users to suppress, shrink, and expand text versions of image maps so
that they may quickly navigate to an image map (which may be, for example, a
navigation tool bar) and decide whether to "expand" it and follow the links of
the map. The metadata listed above will allow users to decide whether to expand
the map. Ensure that the user can expand and shrink the map and navigate its
links using the keyboard and other input devices.
Frames were originally designed so that authors could divide up graphic real
estate and allow the pieces to change independently (e.g., selecting an entry
in a table of contents in one frame changes the contents of a second frame).
While frames are not inherently inaccessible, they raise some accessibility
issues:
- Equivalents to frame content. Some users cannot make use of frames because
they cannot grasp the (spatial or logical) relationships conveyed by frame
layout. Others cannot use them because their user agents or assistive
technology does not support them or makes access difficult (e.g., users with
screen readers or screen magnifiers).
- Navigation. Users need to be able to navigate from frame to frame in a
device independent manner.
- Orientation. Users need to know what frame they are in (so, for example,
authors should provide a title for each frame), what other frames are
available, and how the frames of a frameset are organized.
- Dynamic changes. Users need to know how the changes they cause in one frame
affect other frames.
To name a frame in HTML, use the following algorithm:
- Use the "title" attribute on
FRAME
, or if not present,
- Use the "name" attribute on
FRAME
, or if not present,
- Use title information of the referenced frame source (e.g., the
TITLE
element of the source HTML document), or
- Use title information of the referenced long description (e.g., what
"longdesc" refers to in HTML), or
- Use frame context (e.g., "Frame 2.1.3" to indicate the path to this frame
in nested framesets).
To make frames accessible, user agents should do the following:
- Make available
conditional content related to frames (e.g., provided by the
HTML 4 NOFRAMES element ([HTML4], section 16.4.1).
- Here is a technique for the case of a frameset that does not contain a
NOFRAMES
element but the individual frames have associated long
descriptions ("longdesc"):
- For each frameset, render the frameset title as an
H1
heading.
- For each frame, render the frame title in an
H2
heading,
followed by the content of the associated long description.
- Create a navigable table of contents according to the (possibly nested)
frameset structure. Each entry in the table of contents should link to a
frameset or frame. The end of the content used for each frame should include a
link back to this table of contents.
- Alert the user when the viewport contains a frameset.
- Render a frameset as a list of links to named frames so the user can
identify the number of frames. The list of links may be nested if framesets are
nested.
- Provide information about the number of frames in the frameset.
- Highlight the frameset with the current focus (e.g., by using a thick
border, by displaying the name of the frameset in the status bar, etc.)
- Allow the user to query the frame with the current focus for metadata about
the frame. Make available the frame title for speech synthesizers and braille
displays. Users may also use information about the number of images and words
in the frame to guess the purpose of the frame. For example, few images and few
words probably indicates a title, more words may indicate an index, many words
may indicate a paragraph.
- Allow navigation between frames (forward and backward through the nested
structure, return to a top-level list of links to frames).
Note: Recall that the user needs to be able to navigate frames through
all supported input devices.
- Alert the user when an action in one frame causes the content of another
frame to change. Allow the user to navigate with little effort to the frame(s)
that changed.
- Authors can suppress scrolling of HTML frames with
scrolling="no"
. In this case, the user agent needs to make available
content that is not in the viewport.
- The user agent may ignore some attributes of the
FRAME element of HTML 4 ([HTML4], section 16.2.2):
"
noresize
", "scrolling
", and
"frameborder
".
Consider renderings of the following document:
Example.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Frameset//EN">
<HTML lang="en">
<HEAD>
<META http-equiv="Content-Type"
content="text/html; charset=iso-8859-1">
<TITLE>Time Value of Money</TITLE>
</HEAD>
<FRAMESET COLS="*, 388">
<FRAMESET ROWS="51, *">
<FRAME src="sizebtn" marginheight="5" marginwidth="1"
name="Size buttons" title="Size buttons">
<FRAME src="outlinec" marginheight="4" marginwidth="4"
name="Presentation Outline"
title="Presentation Outline">
</FRAMESET>
<FRAMESET ROWS="51, 280, *">
<FRAME src="navbtn" marginheight="5" marginwidth="1"
name="Navigation buttons"
title="Navigation buttons">
<FRAME src="slide001" marginheight="0" marginwidth="0"
name="Slide Image" title="Slide Image">
<FRAME src="note001" name="Notes" title="Notes">
</FRAMESET>
<NOFRAMES>
<P>List of Presentation Slides</P>
<OL>
<LI><A HREF="slide001">Time Value of Money</A>
<LI><A HREF="slide002">Topic Overview</A>
<LI><A HREF="slide003">Terms and Short Hand</A>
<LI><A HREF="slide004">Future Value of a Single CF</A>
<LI><A HREF="slide005">Example 1: FV example:The
NBAs new Larry Bird exception</A>
<LI><A HREF="slide006">FV Example: NBAs Larry
Bird Exception (cont.)</A>
<LI><A HREF="slide007">SuperStars Contract
Breakdown</A>
<LI><A HREF="slide008">Present Value of a Single
Cash Flow</A>
<LI><A HREF="slide009">Example 2: Paying Jr, and
A-Rod</A>
<LI><A HREF="slide010">Example 3: Finding Rate of
Return or Interest Rate</A>
<LI><A HREF="slide011">Annuities</A>
<LI><A HREF="slide012">FV of Annuities</A>
<LI><A HREF="slide013">PV of Annuities</A>
<LI><A HREF="slide014">Example 4: Invest Early in
an IRA</A>
<LI><A HREF="slide015">Example 4 Solution</A>
<LI><A HREF="slide016">Example 5: Lotto Fever
</A>
<LI><A HREF="slide017">Uneven Cash Flows: Example
6:Fun with the CF function</A>
<LI><A HREF="slide018">Example 6 CF worksheet inputs</A>
<LI><A HREF="slide019">CF inputs continued</A>
<LI><A HREF="slide020">Non-Annual Interest
Compounding</A>
<LI><A HREF="slide021">Example 7: What rate are
you really paying?</A>
<LI><A HREF="slide022">Nominal to EAR Calculator</A>
<LI><A HREF="slide023">Continuous Interest Compounding</A>
<LI><A HREF="slide024">FV and PV with non-annual
interest compounding</A>
<LI><A HREF="slide025">Non-annual annuities</A>
<LI><A HREF="slide026">Example 8: Finding Monthly
Mortgage Payment</A>
<LI><A HREF="slide027">solution to Example 8</A>
</OL>
</NOFRAMES>
</FRAMESET>
</HTML>
The following examples show how some user agents handle this frameset.
Rendering by Lynx
[LYNX]:
Example.
Time Value of Money
FRAME: Size buttons
FRAME: Presentation Outline
FRAME: Navigation buttons
FRAME: Slide Image
FRAME: Notes
List of Presentation Slides
1. Time Value of Money
2. Topic Overview
3. Terms and Short Hand
4. Future Value of a Single CF
5. Example 1: FV example:The NBA's new Larry Bird exception
6. FV Example: NBA's Larry Bird Exception (cont.)
7. SuperStar's Contract Breakdown
8. Present Value of a Single Cash Flow
9. Example 2: Paying Jr, and A-Rod
10. Example 3: Finding Rate of Return or Interest Rate
11. Annuities
12. FV of Annuities
13. PV of Annuities
14. Example 4: Invest Early in an IRA
15. Example 4 Solution
16. Example 5: Lotto Fever
17. Uneven Cash Flows: Example 6:Fun with the CF function
18. Example 6 CF worksheet inputs
19. CF inputs continued
20. Non-Annual Interest Compounding
21. Example 7: What rate are you really paying?
22. Nominal to EAR Calculator
23. Continuous Interest Compounding
24. FV and PV with non-annual interest compounding
25. Non-annual annuities
26. Example 8: Finding Monthly Mortgage Payment
27. solution to Example 8
User agents may also indicate the number of frames in a document and which
frame has the current focus via the menu bar or popup menus. Users can
configure the user agent to include a FRAMES menu item in their menu bar. The
menu bar makes the information highly visible to all users and is very
accessible to assistive technologies.
To make a form accessible, the user agent needs to ensure that:
- the user can navigate to all of the form elements;
- information about the form and its elements is available on demand;
- the user can interact with all form elements through the keyboard alone (or
voice alone or pointing device alone).
- Allow users to navigate to forms and to all controls within a form (refer
also to table navigation techniques). Opera
[OPERA]
and Navigator [NAVIGATOR] provide such
functionality in a non-interactive manner, a "form navigation" keyboard
commands. When invoked, these "form navigation" commands move the user agent's
current
focus to the first form element (if any) in the document.
- If there are no forms in a document and the user attempts to navigate to a
form, alert the user.
- Provide a navigable, structured view of form elements (e.g., those grouped
by
LEGEND
or OPTGROUP
in HTML) along with their
labels.
- Allow the user to navigate away from a menu without selecting any option
(e.g., by pressing the Escape key).
Provide the following information about forms on demand:
- The number of forms in the document.
- The percentage of a form that has already been filled out. This will help
users with serial access to form controls know whether they have completed the
form. Otherwise, users who encounter a submit button that is not the last
control of the form might inadvertently submit the incomplete form.
In conjunction with navigation:
- As the user navigates to a form element, provide information about whether
the control has to be activated before form submission.
- For labels associated with form elements in markup (e.g., the
"
for
" attribute on LABEL
in HTML), make available
label information when the user navigates among the form elements.
- As the user navigates to a form element, provide information (e.g., through
context-sensitive help) about how the user can activate the element. Provide
information about what is required for each form element. Lynx [LYNX] conveys this
information by providing information about the currently selected form element
via a status line message:
- Radio Button: Use right-arrow or Return to toggle
- Checkbox Field: Use right-arrow or Return to toggle
- Option List: Press return and use arrow keys and return to select
option
- Text Entry Field: Enter Text. Use Up or Down arrows
or Tab to move off
- Textarea: Enter text. Up or Down arrows or
Tab to move off (^Ve for editor) Note: The
^Ve (caret-V, e) command, included in the
TEXTAREA
status line message, enables the user to invoke an external
editor defined in the local Lynx configuration file (lynx.cfg).
Provide the following information about the elements in a form on demand
(e.g., for the element with focus):
- Indicate the number of elements in the form.
- Indicate the number of elements that have not yet been completed.
- Provide a list of elements that have to be activated before form
submission.
- Provide information about the order of form elements (e.g., as specified by
"
tabindex
" in HTML). This is important since:
- Most forms are visually oriented, employing changes in font size and
color.
- Users who access forms serially need to know they have supplied all the
necessary information before submitting the form.
- Provide information about which element has focus (e.g., "element X of Y
for the form named MyForm"). The form name is very important for documents that
contain more than one form. This will help users with serial access to form
elements know whether they have completed the form.
- Allow the user to query a form element for information about title, value,
grouping, type, status, and position.
- When a group of radio buttons receives
content focus, identify the radio button with content focus as
"Radio Button X of Y", where "Y" represents the total number of radio buttons
in the group. HTML 4 specifies the
FIELDSET
element ([HTML4], section 17.10), which
allows authors to group thematically related elements and labels. The
LEGEND
element ([HTML4], section 17.10) assigns a
caption to a FIELDSET
. For example, the LEGEND
element might identify a FIELDSET
of radio buttons as "Connection
Rate". Each button could have a
LABEL
element ([HTML4], section 17.9.1) stating a
rate. When it receives content focus, identify the radio button as "Connection
Rate: Radio button X of Y: 28.8kpbs", where "Y" represents the total number of
radio buttons in the grouping and "28.8kbps" is the information contained in
the LABEL
.
- Allow the user to invoke an external editor instead of editing directly in
a
TEXTAREA
element. This allows users to use all the features of
the external editor: macros, spell-checkers, validators, known input
configurations, backups and local copies, etc.
- Provide an option for transforming menus into checkboxes or radio buttons.
In the transformation, retain the accessibility information specified by the
author for the original form elements. Preserve the labels provided for the
OPTGROUP
and each individual OPTION
, and re-associate
them with the generated checkboxes. The LABEL
defined for the
OPTGROUP
should be converted into a LEGEND
for the
result FIELDSET
, and each checkbox should retain the
LABEL
defined for the corresponding OPTION
. Lynx [LYNX] does this for
HTML SELECT
elements that have the "multiple
"
attribute specified.
User agents may help orient users by generating additional content that
"announces" a context change. This may be done through CSS 2 [CSS2] style sheets
using a combination of selectors (including the
':before' and ':after' pseudo-elements described in section 12.1) and the
'content' property (section 12.2).
For instance, the user might choose to hear "language:German" when the natural
language changes to German and "language:default" when it changes
back. This may be implemented in CSS 2 with the
':before' and ':after' pseudo-elements ([CSS2], section 5.12.3)
Example.
With the following definition in the stylesheet:
[lang|=es]:before { content: "start Spanish "; }
[lang|=es]:after { content: " end Spanish"; }
the following HTML example:
<p lang="es" class="Spanish">
<a href="foo_esp.html"
hreflang="es">Esta pagina en español</a></p>
might be spoken "start Spanish _Esta pagina en espanol_ end Spanish". Refer
also to
information on matching attributes and attribute values useful for language
matching in CSS 2 ([CSS2], section 5.8.1).
The following example uses style sheets to distinguish visited from
unvisited links with color and a text
prefix.
Example.
The phrase "Visited link:" is inserted before every visited link:
A:link { color: red } /* For unvisited links */
A:visited { color: green } /* For visited links */
A:visited:before { content: "Visited link: " }
To hide content, use the CSS
'display' or
'visibility' properties ([CSS2], sections 9.2.5 and 11.2,
respectively). The 'display' property suppresses rendering of an entire
subtree. The 'visibility' property causes the user agent to generate a
rendering structure, but the content is invisible.
The following XSLT style sheet (excerpted from the XSLT Recommendation
[XSLT],
Section 7.7) shows how one might number H4 elements in HTML
with a three-part label.
Example.
<xsl:template match="H4">
<fo:block>
<xsl:number level="any" from="H1" count="H2"/>
<xsl:text>.</xsl:text>
<xsl:number level="any" from="H2" count="H3"/>
<xsl:text>.</xsl:text>
<xsl:number level="any" from="H3" count="H4"/>
<xsl:text> </xsl:text>
<xsl:apply-templates/>
</fo:block>
</xsl:template>
End example.
When generating repair
content, user agent developers should consider the following
issues:
- Not all repair content appears in the document
object.
- Users may want to distinguish content (in the document object) provided by the author from
content generated by the user agent. For example, the user may trust
author-supplied content more than generated content.
- Repair content inserted in the document
object should conform to the Web Content Accessibility Guidelines
1.0
[WCAG10]. For example, if the user agent inserts a graphical icon in
the document
object model, that icon should have a text equivalent: since the icon is known to the
user agent developer, the developer can provide a sensible text equivalent to
accompany it (for the benefit of users of assistive technologies).
- Notification of user agent-initiated changes to the document object model may be made through "DOM
events" (refer to the "Document Object Model (DOM) Level 2 Events
Specification" [DOM2EVENTS]).
See also the section on table cell header repair
strategies. Refer also to the W3C document "Techniques for Authoring Tool
Accessibility Guidelines 1.0" [ATAG10-TECHS].
User agents need to make dynamic content accessible to users who may be
disoriented by changes in content, who may have a physical disability that
prevents them from interacting with a document within a time interval specified
by the author, or whose user agent does not support scripts or applets. Not only do user agents make available
equivalents to dynamic content, they have to allow users to turn off
scripts, to stop
animations, adjust timing parameters, etc. Some user agents also
allow users to turn off scripts for security reasons.
Certain elements of a markup language may have associated event handlers
that are activated when certain events occur. User agents need to be able to
identify those elements with event handlers statically associated (i.e.,
associated in the content,
not in a script). In HTML 4 ([HTML4], section 18.2.3),
intrinsic events are specified by the attributes beginning with the prefix
"on": "onblur
", "onchange
", "onclick
",
"ondblclick
", "onkeydown
", "onkeypress
",
"onkeyup
", "onload
", "onmousedown
",
"onmousemove
", "onmouseout
",
"onmouseover
", "onmouseup
", "onreset
",
"onselect
", "onsubmit
", and
"onunload
".
Techniques for providing access to scripts include the following:
- Allow the user to configure the user agent so that mouseover/mouseout event
handlers are activated by (and activate) focus/blur events. Similarly, allow
the user to use a key command, such as "enter" and
"Shift-enter" to fire "
onclick
" and
"ondblclick
" events.
- Implement "Document Object Model (DOM) Level 2 Events Specification"
[DOM2EVENTS] events with a single activation event and provide a
method for firing that event with each supported input device or input API.
These should be the same as the click events and mappings provided above (but
note that a user agent which is also an editor may wish to use single click
events for moving a system caret, and want to provide a different behavior to
activate using the mouse). For example, Amaya [AMAYA] uses a "doAction" command
for activating links and form elements, which can be activated either by the
mouse (and it is possible to set it for single-click or double-click) or by the
keyboard (it is possible to set it for any key using Amaya's keyboard
configuration)
- For authors: Document the effects of known important scripts to give users
an idea in advance of what they do.
When a user agent loads an applet, it
should support the Java system conventions for loading an assistive technology
(see the appendix on loading assistive technologies for
DOM access). If the user is accessing the applet through an assistive
technology, the assistive technology should alert the user when the applet
receives content
focus as this will likely result in the launch of an associated
plug-in or browser-specific Java Virtual Machine. The user agent then needs to
turn control of the applet over to the assistive technology. User agents need
to make
conditional content available to the assistive technology. Applets
generally include an application frame that provides title information.
User agents that allow users to modify default input configurations need to
account for configuration information from several sources: user agent
defaults, user preferences, author-specified configurations, and
operating environment conventions. In HTML, the author may specify
keyboard bindings with the
"accesskey" attribute ([HTML4], section 17.11.2). Users
generally specify their preferences through the user interface but may also do
so programmatically or through a profile.
The user agent may also consider user preferences set at the
operating environment level.
To the user, the most important information is the final configuration once
all sources have been cascaded (combined) and all conflicts resolved. Knowing
the default configuration is also important; checkpoint 12.3 requires
that the default configuration be documented. The user may also want to know
how the current configuration differs from the default configuration and what
configuration in the viewport with the current focus comes from the author.
This information may also be useful to technical support personnel who may be
assisting users.
- The user interfaces for viewing and editing the input configuration may be
combined, but need not be. When a single interface is available to the user,
allow the user to apply filters to the list of bindings (e.g., author-specified
only, user agent default, user preference, final configuration, etc.).
- The user interfaces for viewing and editing the input configuration needs
to be accessible: do not rely on color alone to convey information, use
conventional controls, allow device-independent input and output, etc.
- In the user interface, associate with each binding a short text description
of the function to be activated. For example, if "Control-P" maps to
a print functionality, a short description might be "Print" or "Print setup".
For author-specified configurations, use available information (e.g., "title")
or use generic descriptions of what action will be taken(e.g., "Follow the link
with this link text").
- Allow users to query user interface controls for pertinent input
configuration information (e.g., what key will activate the
functionality).
In general, user preferences should override other configurations, however
this may not always be desirable. For example, users should be prevented from
configuring the user agent in a way that would interfere with important
functionalities such as quitting the user agent or reconfiguring it.
Some options for resolving conflicts:
- Allow author configurations to override other configurations and alert the
user when this happens.
- Do not allow author configurations to override other configurations. Alert
the user when an author-specified binding has been overridden and provide
access to the author-specified control through other means (e.g., an unused
binding, a menu, in a list of all author-specified bindings, etc.)
- Author-specified keyboard bindings in combination with the user agent's
native configuration may conflict with operating environment conventions. For example,
Internet Explorer
[IE-WIN] in Windows uses the Alt key as the compose key
for author-specified bindings. If the author has specified a configuration with
the characters "h" or "f", this will interfere with the
operating environment conventions for accessing help and the file
menu. In addition to the previous two options for handling conflicts, the user
agent may allow the user to choose another compose key (either
globally or on a per-document basis when conflicts are
detected).
The following techniques apply to user agents that render content as
synthesized speech.
- Since user agents that render content as speech do not always pronounce it
correctly, they should provide additional context to facilitate understanding.
Techniques include:
- Spelling words
- Indicating punctuation, capitalization, etc.
- Allowing users to repeat words alone and in context.
- Using auditory nuances – including pitch, articulation model, volume,
and orientation – to convey meaning the way fonts, spacing, and borders
do in
graphical media.
- Generating context. For example, a user agent might speak the word "link"
before a link, "heading" before the text content
of a heading or "item 1.4" before a list item.
- Rendering
text according in the appropriate natural
language.
- User agents that synthesize speech should implement the CSS 2 aural style
sheet properties ([CSS2], section 19) to allow users to
configure speech rate, volume, and pitch.
- User agents that provide accessible solutions for images should, by
default, provide no information about images where the author has
provided empty
conditional content associated with the image, otherwise information
may clutter the user's view of the content and cause confusion. The user should
be able to turn off this option.
- User agents may recognize
different natural
languages and be able to render content according to language markup
defined for a certain part of the document. For instance, a screen reader might
change the pronunciation of spoken text according to the language definition.
This is usually desired and done according to the capabilities of the tool.
Some specialized tools might give some finer user control for the pronunciation
as well.
- Switching natural languages for blocks of content may be more helpful than
switching for short phrases. In some language combinations (e.g., Japanese
being the primary and English being the secondary or quoted language), short
foreign language phrases are often well-integrated in the primary language.
Dynamic switching for these short phrases may make the content sound unnatural
and possibly harder to understand. User agents might allow users to choose
elements for which they want to be alerted.
- The following techniques for speaking data tables are adapted from the
"Tape Recording Manual" produced by the National Braille Association [NBA]:
- Read the title, source, captions
and any explanatory keys.
- Describe the structure of the table. Include the number of columns, the
headers of each column and any associated sub-columns, reading from left to
right. The subhead is not considered a column. If column heads have footnotes,
read them following each header.
- Explain whether the table will be read by rows (horizontally) or by columns
(vertically). The horizontal reading is usual but, in some cases, the vertical
reading better conveys the content. On rare occasions it is necessary to read a
table both ways.
- Repeat the column headers with the figures under them for the first two
rows. If the table is long, repeat the headers every fifth row. Always repeat
them during the reading of the last row.
- Indicate the last row by saying, "and finally . . . " or "last row
..."
- At the completion of the reading say "End table X." If the table appeared
on a page other than the one you were recording, add "Returning to text on page
Y."
References:
- For more information about voice browser technology developed at W3C, refer
to "Voice Browsers: An introduction and glossary for the requirements drafts"
[VOICEBROWSER].
- For information about speech recognition and accessibility, refer to "Speak
to Write" [SPEAK2WRITE].
Some interactions with content may require spatial information, often
provided by users without disabilities through a pointing device such as a
mouse.
- User agents should not require users to "move through space" to interact
with content (or "time", for that matter; see checkpoint 2.4). Thus, for users without a pointing device,
the user agent's first approximation of access, say through the keyboard, would
be to simulate the mouse with keystrokes. However, such a technique usually
requires a significant amount of visual feedback as well as physical dexterity,
both of which may not be possible for users with some disabilities.
- A better alternative is to allow users to enter coordinates where a click
should occur. While this is "direct access" to the coordinate, this requires
extensive knowledge of the geometry in question.
- A still better alternative is to allow the user to interact with "objects"
in content at a more abstract level than geometry. For example, most HTML
authors can use "client-side" image maps rather than "server-side" since what
is important is not the actual coordinates but rather that the user has
selected one region instead of another. The user agent should convey
information about the regions, using descriptions provided by the author.
Instead of having users choose a state of the United States by its precise
longitude and latitude, it is possible to allow them to choose state by
name.
The following techniques may be considered when integrating accessibility
features and internationalization.
- Implement content negotiation so that users may specify language
preferences. Or allow the user to choose manually from among related resources
available in different languages.
- Consider
operating environment level natural language preferences as the
user's default language preference. However, take caution about sending HTTP
Accept-Language request headers ([RFC2616], section 14.4) based on
the operating environment preferences. First, there may be a privacy problem as
indicated in RFC 2616, section 15.1.4 "Privacy Issues Connected to Accept
Headers". Also, the operating environment may define only one language, while
the Accept-Language request header may include many languages in different
priorities. Setting Accept-Language to be the operating environment language
may prevent a user from receiving content from a server that does not have a
match for this particular language but does for other languages acceptable to
the user.
- Render characters with the appropriate directionality. Refer to the
"dir" attribute and the
BDO element in HTML 4 ([HTML4], sections 8.2 and 8.2.4
respectively). Refer also to the Unicode specification
[UNICODE].
This matrix summarizes which checkpoints are expected to benefit users with
certain types of disabilities. For more information about types of
disabilities, assistive technologies, access strategies, and more, refer to
"How People with Disabilities Use the Web" [PWD-USE-WEB].
Several operating systems include built-in accessibility features designed
to assist individuals with varying abilities. Despite operating systems
differences, the built-in accessibility features use a similar naming
convention and offer similar functionalities, within the limits imposed by each
operating system (or particular hardware platform). The following is a list of
built-in accessibility features from several platforms:
- StickyKeys
- StickyKeys allows users who have difficulties with pressing several keys
simultaneously to press and release sequentially each key of the
configuration.
- MouseKeys
- These allow users to move the mouse cursor and activate the mouse button(s)
from the keyboard.
- RepeatKeys
- RepeatKeys allows users to set how fast a key repeats ("repeat rate") when
the key is held pressed. It also allows users to control how quickly the key
starts to repeat after the key has been pressed ("delay until repeat"). Users
can also turn off key repeating.
- SlowKeys
- SlowKeys instructs the computer not to accept a key as pressed until it has
been pressed and held down for more than a user-configurable length of
time.
- BounceKeys
- BounceKeys prevents extra characters from being typed if the user bounces
(e.g., due to a tremor) on the same key when pressing or releasing it.
- ToggleKeys
- ToggleKeys provides an audible indication for the status of keys that have
a toggled state (keys that maintain status after being released). The most
common toggling keys include Caps Lock, Num Lock, and Scroll Lock.
- SoundSentry
- SoundSentry monitors the operating system and applications for sounds in
order to provide a graphical
indication when a sound is being played. Older versions of SoundSentry may have
flashed the entire display screen for example, while newer versions of
SoundSentry provide the user with a selection of options, such as flashing the
viewport that has the current focus or flashing the active window caption
bar.
The next three built-in accessibility features are not as commonly available
as the above group of features, but are included here for definition,
completeness, and future compatibility.
- ShowSounds
- ShowSounds are user settings or software switches that cause audio to be
presented using both audio and graphics. Applications may use these switches as
the basis of user preferences.
- HighContrast
- HighContrast sets fonts and colors designed to make the screen easier to
read.
- TimeOut
- TimeOut turns off built-in accessibility features automatically if the
computer remains idle for a user-configurable length of time. This is useful
for computers in public settings such as a library. TimeOut might also be
referred to as "reset" or "automatic reset".
The next accessibility feature listed here is not considered to be a
built-in accessibility feature (since it only provides an alternative input
channel) and is presented here only for definition, completeness, and future
compatibility.
- SerialKeys
- SerialKeys allows a user to perform all keyboard and mouse functions from
an external assistive device (such as communication aid) communicating with the
computer via a serial character stream (e.g., serial port, infra-red port,
etc.) rather than or in conjunction with, the keyboard, mouse, and other
conventional input devices/methods.
The following accessibility features can be adjusted from the Accessibility
Options Control Panel:
- StickyKeys: modifier keys include Shift, Control, and
Alt.
- FilterKeys: grouping term for SlowKeys, RepeatKeys, and BounceKeys.
- MouseKeys
- ToggleKeys
- SoundSentry
- ShowSounds
- Automatic reset: term used for TimeOut
- High Contrast
- SerialKeys
Additional accessibility features available in Windows 98:
- Magnifier
- Magnifier is a windowed, screen enlargement and enhancement program used by
people with low vision to magnify an area of the
graphical display (e.g., by tracking the text cursor,
current focus, etc.). Magnifier can also
invert the colors used by the system within the magnification window.
- Accessibility Wizard
- The Accessibility Wizard is a setup tool to assist users with the
configuration of system accessibility features.
References:
- To find out about built-in accessibility features on Windows platforms, ask
the system via the "SystemParametersInfo" function. Please refer to "Software
accessibility guidelines for Windows applications"
[MS-ENABLE] for more information.
- For information about Microsoft keyboard configurations (Internet Explorer,
Windows 95, Windows 98, and more), refer to documentation on keyboard
assistance for Internet Explorer and MS Windows
[MS-KEYBOARD].
The following accessibility features can be adjusted from the Easy Access
Control panel. Note: The Apple naming convention for accessibility features is to put spaces between
the terms (e.g., "Sticky Keys" instead of "StickyKeys").
- Sticky Keys: modifier keys include the Shift, Command
(Open apple), Option (Alt), and
Control keys.
- Slow Keys
- Mouse Keys
The following accessibility features can be adjusted from the Keyboard
Control Panel.
- Key Repeat Rate (part of RepeatKeys)
- Delay Unit Repeat (part of RepeatKeys)
The following accessibility feature can be adjusted from the Sound or
Monitors and Sound Control Panel (depending on system version).
- Adjusting the volume to off or mute causes the Macintosh to flash the title
bar whenever the operating system detects a sound (e.g., SoundSentry)
Additional accessibility features available for the Macintosh OS:
- CloseView
- CloseView is a full screen, screen enlargement and enhancement program used
by people with low vision to magnify the information on the graphical display,
and it can also change the colors used by the system.
- SerialKeys
- SerialKeys is available as freeware from Apple and several other Web
sites.
The following accessibility features can be adjusted from the AccessX
graphical user interface X client on some DEC, SUN, and SGI operating systems.
Other systems supporting XKB may require the user to manipulate the features
via a command line parameter(s).
- StickyKeys: modifier keys are platform-dependent, but usually include the
Shift, Control, and Meta keys.
- RepeatKeys
- SlowKeys
- BounceKeys
- MouseKeys
- ToggleKeys
Note: AccessX became a supported part of the X Window
System X Server with the release of the X Keyboard Extension in version
X11R6.1
The following accessibility features are available from a freeware program
called AccessDOS, which is available from several Internet Web sites including
IBM, Microsoft, and the Trace Center, for either PC-DOS or MS-DOS versions 3.3
or higher.
- StickyKeys: modifier keys include the Shift, Control,
and Alt keys.
- Keyboard Response Group: grouping term for SlowKeys, RepeatKeys, and
BounceKeys
- MouseKeys
- ToggleKeys
- SoundSentry (incorrectly named ShowSounds)
- SerialKeys
- TimeOut
Many of the checkpoints in the guidelines require a "host" user agent to
communicate information about content and the user interface to assistive
technologies. This appendix explains how developers can ensure the timely
exchange of this information (see checkpoint 6.9). The techniques described here include:
- Loading the entire assistive technology in the
address space of the host user agent;
- Loading part of the assistive technology in the
address space of the host user agent (e.g., piece of stub code, a dynamically
linked library (DLL), a browser helper
object, etc.);
- Out-of-process access to the
document object model.
The first two techniques are similar, differing in the amount of, or
capability of, the assistive technology loaded in the same process or address
space as the host user agent. These techniques are likely to provide faster
access to the document
object model since they will not be subject to inter-process
communication overhead.
Note: This appendix does not address specialized user
agents.
First, the host user agent needs to know which assistive technology to load.
One technique for this is to store a reference to an assistive technology in a
system registry file or, in the case of Java, a properties file. Registry files
are common among many operating system platforms:
- Windows: use the system registry file
- IBM OS/2: use the system.ini
- On client/server systems: use a system registry server that an application
running on the network client computer can query.
- In Sun Java 2, use the "accessibility.properties" file, which causes the
system event queue to examine the file for assistive technologies required for
loading. If the file contains a property called "assistive_technologies", it
will load all registered assistive technologies and start them on their own
thread in the Java Virtual Machine that is a single process.
Here is an example entry for Java:
assistive_technologies=com.ibm.sns.svk.AccessEngine
In Microsoft Windows, a similar technique could be followed by storing the
name of a Dynamic Link Library (DLL) for an assistive
technology in a designated assistive technology key name/assistive technology
pair.
Here is an example entry for Windows:
HKEY_LOCAL_MACHINE\Software\Accessibility\DOM
"ScreenReader, VoiceNavigation"
Once the assistive technology has been registered, any other user agent can
determine whether it needs to be loaded and then load it. Once loaded, the
assistive technology can monitor the document
object model as needed.
On a non-Java platform, a technique to do this would be to create a separate
thread with a reference to the document object model using a
DLL. This new thread will load the DLL and call a
specified DLL entry name with a pointer to the document object model interface.
The assistive technology process will then run as long as required.
The assistive technology has the option to either:
- communicate with a main assistive technology of its own and process the
document object model as a caching mechanism for the main assistive technology,
or
- act as a bridge to the document object model for the main assistive
technology.
In the future, it will be necessary to provide a more comprehensive
reference to the application that not only provides direct navigation to its
client area document object model, but also multiple document object models
that it is processing and an event model for monitoring them.
Java can facilitate timely access to accessibility components. In this
example, an assistive technology running on a separate thread monitors user
interface events such as focus
changes. When focus changes, the assistive technology is alerted of which
component object has focus. The assistive technology can communicate directly
with all components in the application by walking the parent/child hierarchy
and connecting to each component's methods and monitor events directly. In this
case, an assistive technology has direct access to component specific methods
as well as those provided for by the Java Accessibility API.
There is no reason that a document object model interface to user agent
components could not be provided via Java.
In Java 1.1.x, Sun's Java access utilities load an assistive by monitoring
the Java awt.properties file for the presence of assistive
technologies and loads them as shown in the following code example:
Example.
import java.awt.*;
import java.util.*;
String atNames = Toolkit.getProperty("AWT.assistive_technologies",null);
if (atNames != null) {
StringTokenizer parser = new StringTokenizer(atNames," ,");
String atName;
while (parser.hasMoreTokens()) {
atName = parser.nextToken();
try {
Class.forName(atName).newInstance();
}
catch (ClassNotFoundException e) {
throw new AWTError("Assistive Technology not found: " + atName);
}
catch (InstantiationException e) {
throw new AWTError("Could not instantiate Assistive" +
" Technology: " + atName);
}
catch (IllegalAccessException e) {
throw new AWTError("Could not access Assistive" +
" Technology: " + atName);
} catch (Exception e) {
throw new AWTError("Error trying to install Assistive" +
" Technology: " + atName + " " + e);
}
}
}
In the above code example, the function
Class.forName(atName).newInstance()
creates a new instance of the
assistive technology. The constructor for the assistive technology will then be
responsible for monitoring application component objects by monitoring system
events.
In the following code example, the constructor for the assistive technology,
AccessEngine
, adds a focus change
listener using Java accessibility utilities. When the assistive technology is
alerted that an object has received focus, it has direct access to that object.
If the Object, o
, has implemented a document object model
interface, the assistive technology will have direct access to the document
object model in the same process space as the application.
Example.
import java.awt.*;
import javax.accessibility.*;
import com.sun.java.accessibility.util.*;
import java.awt.event.FocusListener;
class AccessEngine implements FocusListener {
public AccessEngine() {
//Add the AccessEngine as a focus change listener
SwingEventMonitor.addFocusListener((FocusListener)this);
}
public void focusGained(FocusEvent theEvent) {
// get the component object source
Object o = theEvent.getSource();
// check to see if this is a document object model component
if (o instanceof DOM) {
...
}
}
public void focusLost(FocusEvent theEvent) {
// Do Nothing
}
}
In this example, the assistive technology has the option of running
stand-alone or acting as a cache for a bridge that communicates with a main
assistive technology running outside the Java virtual machine.
In order to attach to a running instance of Internet Explorer 4.0, you can
use a Browser Helper Object ([BHO]), which is a DLL
that will attach itself to every new instance of Internet Explorer 4.0 [IE-WIN] (only
if you run iexplore.exe). You can use this feature to gain access to the object
model of Internet Explorer and to monitor events. This can be tremendously
helpful when many method calls need to be made to IE, as each call will be
executed much more quickly than the out of process case.
There are some requirements when creating a Browser Helper Object:
- The application that you create must be an in-process server (that is,
DLL).
- This DLL must implement
IObjectWithSite
.
- The
IObjectWithSite::SetSite()
method must be implemented. It
is through this method that your application receives a pointer to Internet
Explorer's IUnknown
. Internet Explorer actually passes a pointer
to IWebBrowser2
but the implementation of SetSite()
receives a pointer to IUnknown
. You can use this
IUnknown
pointer to automate Internet Explorer or to sink events from
Internet Explorer.
- It must be registered as a Browser Helper Object as described above.
To provide native Microsoft Windows assistive technologies access to Java
applications without creating a Java native solution, Sun Microsystems provides
the "Java Access Bridge." This bridge is loaded as an assistive technology as
described in the section on loading assistive
technologies for direct navigation of the document object model. The bridge
uses a Java Native Invocation (JNI) to Dynamic Link Library
(DLL) communication and caching mechanism that allows a
native assistive technology to gather and monitor accessibility information in
the Java environment. In this environment, the assistive technology determines
that a Java application or applet is running and communicates with the Java
Access Bridge DLL to process accessibility information about
the application/applet running in the Java Virtual Machine.
Access to application specific data across process boundaries or address
space might be costly in terms of performance. However, there are other reasons
to consider when accessing the document
object model that might lead a developer to wish to access it from
their own process or memory address space. One obvious protection this method
provides is that, if the user agent fails, it does not disable the user's
assistive technology as well. Another consideration would be legacy systems,
where the user relies on their assistive technology for access to software
other than the user agent, and thus would have their application loaded all the
time.
There are several ways to gain access to the user agent's document object model. Most user agents support
some kind of external interface, or act as a mini-server to other applications
running on the desktop. Internet Explorer [IE-WIN] is a good example of this,
as IE can behave as a component object model (COM) server to
other applications. Mozilla [MOZILLA], the open source release
of Navigator also supports cross platform COM (XPCOM).
The following example illustrates the use of COM to access the IE object
model. This is an example of how to use COM to get a pointer to the
WebBrowser2
module, which in turn enables access to an interface/pointer
to the document object, or IE document object model for the content.
Example.
/* first, get a pointer to the WebBrowser2 control */
if (m_pIE == NULL) {
hr = CoCreateInstance(CLSID_InternetExplorer,
NULL, CLSCTX_LOCAL_SERVER, IID_IWebBrowser2,
(void**)&m_pIE);
/* next, get a interface/pointer to the document in view,
this is an interface to the document object model (DOM)*/
void CHelpdbDlg::Digest_Document() {
HRESULT hr;
if (m_pIE != NULL) {
IDispatch* pDisp;
hr = m_pIE->QueryInterface(IID_IDispatch, (void**) &pDisp);
if (SUCCEEDED(hr)) {
IDispatch* lDisp;
hr = m_pIE->get_Document(&lDisp);
if (SUCCEEDED(hr)) {
IHTMLDocument2* pHTMLDocument2;
hr = lDisp->QueryInterface(IID_IHTMLDocument2,
(void**) &pHTMLDocument2);
if (SUCCEEDED(hr)) {
/* with this interface/pointer, IHTMLDocument2*,
you can then work on the document */
IHTMLElementCollection* pColl;
hr = pHTMLDocument2->get_all(&pColl);
if (SUCCEEDED(hr)) {
LONG c_elem;
hr = pColl->get_length(&c_elem);
if (SUCCEEDED(hr)) {
FindElements(c_elem, pColl);
}
pColl->Release();
}
pHTMLDocument2->Release();
}
lDisp->Release();
}
pDisp->Release();
}
}
}
}
For a working example of this method, refer to HelpDB [HELPDB].
This glossary is
normative. Some terms (or parts of explanations of terms) may not
have an impact on conformance.
Note: In this document, glossary terms generally link to
the corresponding entries in this section. These terms are also highlighted
through style sheets and identified as glossary terms through markup.
- Activate
- In this document, the verb "to activate" means (depending
on context) either:
The effect of activation depends on the type of enabled element or user
interface control. For instance, when a link is activated, the user agent
generally retrieves the linked Web
resource. When a form element is activated, it may change state
(e.g., check boxes) or may take user input (e.g., a text entry field).
-
Alert
- In this document, "to alert" means to make the user aware
of some event, without requiring acknowledgement. For example, the user agent
may alert the user that new content is available on the server by displaying a
text message in the user agent's status bar.
See checkpoint 1.3 for
requirements about alerts.
-
Animation
- In this document, the term "animation" refers to any
visual movement effect created automatically (i.e., without manual user
interaction). This definition of animation includes video and animated images.
Animation techniques include:
- graphically displaying a sequence of snapshots within the same region
(e.g., as is done for video and animated images). The series of snapshots may
be provided by a single resource (e.g., an animated GIF image) or from distinct
resources (e.g., a series of images downloaded continuously by the user
agent).
- scrolling text (e.g., achieved through markup or style sheets).
- displacing graphical objects around the viewport (e.g., a picture of a ball
that is moved around the viewport giving the impression that it is bouncing off
of the viewport edges). For instance, the SMIL 2.0 [SMIL20] animation modules explain
how to create such animation effects in a declarative manner (i.e., not by
composition of successive snapshots).
-
Applet
- An applet is a program (generally written in the Java
programming language) that is part of content,
and that the user agent executes.
- Application
Programming Interface (API), conventional input/output/device
API
- An application programming interface (API) defines how
communication may take place between applications.
Implementing APIs that are independent of a particular operating environment
(as are the W3C DOM Level 2 specifications) may reduce implementation costs for
multi-platform user agents and promote the development of multi-platform
assistive technologies. Implementing conventional APIs for a particular
operating environment may reduce implementation costs for assistive technology
developers who wish to interoperate with more than one piece of software
running on that operating environment.
A "device API" defines how communication may take place
with an input or output device such as a keyboard, mouse, video card, etc.
In this document, an "input/output API" defines how
applications or devices communicate with a user agent. As used in this
document, input and output APIs include, but are not limited to, device APIs.
Input and output APIs also include more abstract communication interfaces than
those specified by device APIs. A "conventional input/output API" is one that
is expected to be implemented by software running on a particular operating
environment. For example, on desktop computers today, the conventional input
APIs are for the mouse and keyboard. For touch screen
devices or mobile devices, conventional input APIs may
include stylus, buttons, voice, etc. The graphical display and sound card are
considered conventional ouput devices for a graphical desktop computer
environment, and each has an associated API.
- Assistive technology
- In the context of this document, an assistive technology
is a
user agent that:
- relies on services (such as retrieving
Web resources, parsing markup, etc.) provided by one or more other
"host" user agents. Assistive technologies communicate data and messages with
host user agents by using and monitoring APIs.
- provides services beyond those offered by the host user agents to meet the
requirements of a users with disabilities. Additional services include
alternative renderings (e.g., as synthesized speech or magnified content),
alternative input methods (e.g., voice), additional navigation or orientation
mechanisms, content transformations (e.g., to make tables more accessible),
etc.
For example, screen reader software is an assistive technology because it
relies on browsers or other software to enable Web access, particularly for
people with visual and learning disabilities.
Examples of assistive technologies that are important in the context of this
document include the following:
- screen magnifiers, which are used by people with visual disabilities to
enlarge and change colors on the screen to improve the visual readability of
rendered text and images.
- screen readers, which are used by people who are blind or have reading
disabilities to read textual information through synthesized speech or braille
displays.
- speech recognition software, which may be used by people who have some
physical disabilities.
- alternative keyboards, which are used by people with certain physical
disabilities to simulate the keyboard.
- alternative pointing devices, which are used by people with certain
physical disabilities to simulate mouse pointing and button activations.
- Beyond this document, assistive technologies consist of
software or hardware that has been specifically designed to assist people with
disabilities in carrying out daily activities, e.g., wheelchairs, reading
machines, devices for grasping, text telephones, vibrating pagers, etc. For
example, the following very general definition of "assistive technology device"
comes from the (U.S.) Assistive Technology Act of 1998 [AT1998]:
Any item, piece of equipment, or product system, whether acquired
commercially, modified, or customized, that is used to increase, maintain, or
improve functional capabilities of individuals with disabilities.
-
Attribute
- This document uses the term "attribute" in the XML sense:
an element may have a set of attribute specifications (refer to the XML 1.0
specification
[XML] section 3).
- Audio-only
presentation
- An audio-only presentation is content consisting
exclusively of one or more audio
tracks presented concurrently or in series. Examples of an
audio-only presentation include a musical performance, a radio-style news
broadcast, and a book reading.
-
Audio track
- An audio object is content rendered as sound through an
audio
viewport. An audio track is an audio
object that is intended as a whole or partial presentation. An audio track may,
but is not required to, correspond to a single audio channel (left or right
audio channel).
- Auditory description
- An auditory description (sometimes, "audio description")
is either a prerecorded human voice or a synthesized voice (recorded or
generated dynamically) describing the key visual elements of a movie or other
animation. The auditory description is
synchronized with the audio
track of the presentation, usually during natural pauses in the audio track. Auditory descriptions include
information about actions, body language, graphics, and scene changes.
-
Author styles
- Authors styles are style property values that come from a
document, or from its associated style sheets, or that are generated by the
server.
- Captions
- Captions (sometimes, "closed captions") are text
transcripts that are
synchronized with other audio
tracks or visual
tracks. Captions convey information about spoken words and
non-spoken sounds such as sound effects. They benefit people who are deaf or
hard-of-hearing, and anyone who cannot hear the audio (e.g., someone in a noisy
environment). Captions are generally rendered
graphically above, below, or superimposed over video.
Note: Other terms that include the word "caption" may have different
meanings in this document. For instance, a "table caption" is a title for the
table, often positioned graphically above or below the table. In this document,
the intended meaning of "caption" will be clear from context.
- Character encoding
- A "character encoding" is a mapping from a character set
definition to the actual code units used to represent the data. Please refer to
the Unicode specification [UNICODE] for more information
about character encodings. Refer to "Character Model for the World Wide Web"
[CHARMOD] for additional information about characters and character
encodings.
- Collated text
transcript
- A collated text transcript is a text equivalent of a movie or other animation.
More specifically, it is the combination of the text transcript of the audio track and the text equivalent of the
visual track. For example, a collated
text transcript typically includes segments of spoken dialogue interspersed
with text descriptions of the key visual elements of a presentation (actions,
body language, graphics, and scene changes). See also the definitions of text
transcript and auditory
description. Collated text transcripts are essential for individuals
who are deaf-blind.
- Conditional content
- Conditional content is content that, by specification,
should be made available to users through the user interface, generally under
certain conditions (e.g., based on user preferences or operating environment
limitations). Some examples of conditional content mechanisms include:
- The "
alt
" attribute of the IMG
element in HTML 4.
According to
section 13.2 of the HTML 4 specification ([HTML4]): "User agents must render
alternate text when they cannot support images, they cannot support a certain
image type or when they are configured not to display images.
OBJECT
elements in HTML 4.
Section 13.3.1 of the HTML 4 specification ([HTML4]) explains the conditional
rendering rules of (nested) OBJECT
elements.
- The
switch
element and test attributes in SMIL 1.0. Sections
4.3 and 4.4, respectively,
of SMIL 1.0
[SMIL] explain the conditional rendering rules of these
features.
- SVG 1.0
[SVG] also includes a
switch
element and several
attributes for conditional processing.
- The
NOSCRIPT
and NOFRAMES
elements in HTML 4
[HTML4]
allow the author to provide content under conditions when the user agent does
not support scripts or frames, or the user has turned off support for scripts
or frames.
Specifications vary in how completely they define how and when to render
conditional content. For instance, the HTML 4 specification includes the
rendering conditions for the "alt
" attribute, but not for the
"title
" attribute. The HTML 4 specification does indicate that the
"title
" attribute should be available to users through the user
interface ("Values of the title attribute may be rendered by user agents in a
variety of ways...").
Note: The Web Content Accessibility Guidelines 1.0 requires
that authors provide text equivalents for non-text content. This is generally
done by using the conditional content mechanisms of a markup language. Since
conditional content may not be rendered by default, the current document
requires the user agent to provide access to unrendered conditional content (checkpoint 2.3 and checkpoint 2.9)
as it may have been provided to promote accessibility.
-
Configure,
control
- In the context of this document, the verbs "to control"
and "to configure" share in common the idea of governance such as a user may
exercise over interface layout, user agent behavior, rendering style, and other
parameters required by this document. Generally, the difference in the terms
centers on the idea of persistence. When a user makes a change by
"controlling" a setting, that change usually does not persist beyond that user
session. On the other hand, when a user "configures" a setting, that setting
typically persists into later user sessions. Furthermore, the term "control"
typically means that the change can be made easily (such as through a keyboard
shortcut) and that the results of the change occur immediately, whereas the
term "configure" typically means that making the change requires more time and
effort (such as making the change via a series of menus leading to a dialog
box, via style sheets or scripts, etc.) and that the results of the change may
not take effect immediately (e.g., due to time spent reinitializing the system,
initiating a new session, rebooting the system). In order to be able to
configure and control the user agent, the user needs to be able to "read" as
well as "write" values for these parameters. Configuration settings may be
stored in a profile.
The range and granularity of the changes that can be controlled or configured
by the user may depend on limitations of the
operating environment or hardware.
Both configuration and control may apply at different "levels": across
Web resources (i.e., at the user agent
level, or inherited from the operating environment), to the entirety of a
Web resource, or to components of a Web resource (e.g., on a per-element
basis).
A
global configuration is one that applies across elements of the
same Web resource, as well as across Web resources. A global configuration may
be implemented by more than one setting (e.g., per component of the user
agent). For instance, when a user agent consists of a browser that renders HTML
and a plug-in that renders SVG, to satisfy the global configuration
requirements of this document, the browser may provide one setting and the plug
another.
User agents may allow users to choose configurations based on various
parameters, such as hardware capabilities, natural language, etc.
Note: In this document, the noun "control" refers to a
component of the user
agent user interface.
-
Content
- In this specification, the noun "content" is used in three
ways:
- It is used to mean the document
object as a whole or in parts.
- It is used to mean the content of an HTML or XML element, in the sense
employed by the XML 1.0 specification ([XML], section 3.1): "The text between
the start-tag and end-tag is called the element's content." Context should
indicate that the term content is being used in this sense.
- It is used in the context of the phrases non-text content and
text content.
Empty
content is either a null value or a string consisting of zero
characters. For instance, in HTML, "alt=''
" sets the value of the
"alt
" attribute to the empty string. In some markup languages, an
element may have empty content.
- Device-independence
- Device-independence refers to the ability to make use of
software with any supported input or output device.
-
Document object,
Document Object Model (DOM)
- In general usage, the term "document object" refers to the user agent's
representation of data (e.g., a document). This data generally comes from the
document
source, but may also be generated (from style sheets, scripts,
transformations, etc.), produced as a result of preferences set within the user
agent, added as the result of a repair performed automatically by the user
agent, etc. Some data that is part of the document object is routinely
rendered (e.g., in HTML, what appears between the start and end tags
of elements and the values of attributes such as "alt", "title", and
"summary"). Other parts of the document object are generally processed by the
user agent without user awareness, such as DTD-defined names of element types
and attributes, and other attribute values such as "href", "id", etc. These
guidelines require that users have access to both types of data through the
user interface. Most of the requirements of this document apply to the document
object after its construction. However, a few checkpoints (e.g., checkpoint 2.7 and checkpoint 2.11) may
affect the construction of the document object.
A "document object model" is the abstraction that governs the construction
of the user agent's document object. The document object model employed by
different user agents may vary in implementation and sometimes in scope. This
specification requires that user agents implement the
APIs defined in Document Object Model
(DOM) Level 2 Specifications ([DOM2CORE] and
[DOM2STYLE]) for access to HTML,
XML, and CSS content. These DOM APIs allow authors
to access and modify the content via a scripting language (e.g., JavaScript) in
a consistent manner across different scripting languages. As a standard
interface, the DOM APIs make it easier not just for authors, but for assistive
technology developers to extract information and render it in ways most suited
to the needs of particular users.
-
Document character set
- A document character set (an concept taken from SGML) is a
sequence of abstract characters that may appear in Web content represented in a
particular format (such as HTML, XML, etc.). A document character set consists
of:
- a "repertoire", A set of abstract characters, such as the Latin letter "A",
the Cyrillic letter "I", the Chinese character meaning "water", etc.
- Code positions: A set of integer references to characters in the
repertoire.
For instance, the character set required by the HTML 4 specification [HTML4] is defined
in the Unicode specification [UNICODE]. Refer to "Character
Model for the World Wide Web" [CHARMOD] for more information
about document character sets.
-
Document source, text source
- In this document, the term "document source" refers to the
data that the user agent receives as the direct result of a request for a
Web resource (e.g., as the result of an
HTTP/1.1
[RFC2616] "GET", or as the result of viewing a resource on the local
file system). The document source generally refers to the "payload" of the user
agent's request, and doesn't generally include information exchanged as part of
the transfer protocol. The document source is data that is prior to any repair
by the user agent (e.g., prior to repairing invalid markup). "Text source"
refers to document source that is composed of
text.
-
Documentation
- Documentation refers to information that supports the use
of a user agent. This information may be found in manuals, installation
instructions, the help system, tutorials, etc. Documentation may be distributed
(e.g., some parts may be delivered on CD-ROM, others on the Web). Refer to guideline 12 for information about
documentation requirements.
- Element
- This document uses the term "element" both in the XML
sense (an element is a syntactic construct as described in the XML 1.0
specification
[XML], section 3) and more generally to mean a type of content (such
as video or sound) or a logical construct (such as a header or list).
-
Enabled element, disabled element
- An enabled element is a piece of
content with associated behaviors that may be activated through the
user interface or through an API. The set of elements that a user agent
enables is generally derived from, but is not limited to, the set of
interactive elements defined by implemented markup languages.
Some elements may only be enabled elements for part of a user session. For
instance, an element may be disabled by a script as the result of user
interaction. Or, an element may only be enabled during a given time period
(e.g., during part of a SMIL 1.0 [SMIL] presentation). Or, the user
may be viewing content in "read-only" mode, which may disable some
elements.
A disabled element is a piece of content
that is potentially an enabled element, but is not in the current session.
Generally, disabled elements will be interactive elements that are not enabled in
the current session. This document distinguishes disabled elements (not
currently enabled) from non-interactive elements (never enabled).
For the requirements of this document, user
selection does not constitute user interaction with enabled
elements. See the definition of content
focus.
Note: Enabled and disabled elements come from content; they
are not part of the user
agent user interface.
Note: The term "active element" is not used in this
document since it may suggest several different concepts, including:
interactive element, enabled element, an element "in the process of being
activated" (which is the meaning of ':active' in CSS2 [CSS2], for example).
-
Equivalent (for content)
- The term "equivalent" is used in this document as it is
used in the Web Content Accessibility Guidelines 1.0 [WCAG10]:
Content is "equivalent" to other content when both fulfill essentially the
same function or purpose upon presentation to the user. In the context of this
document, the equivalent must fulfill essentially the same function for the
person with a disability (at least insofar as is feasible, given the nature of
the disability and the state of technology), as the primary content does for
the person without any disability.
Equivalents include text
equivalents (e.g., text equivalents for images; text transcripts for
audio tracks; collated text transcripts for multimedia presentations and
animations) and non-text
equivalents (e.g., a prerecorded auditory description of a
visual track of a movie, or a sign
language video rendition of a written text, etc.).
Each markup language defines its own mechanisms for specifying
conditional content, and these mechanisms may be used by authors to
provide text equivalents. For instance, in HTML 4 [HTML4] or SMIL 1.0 [SMIL], authors may
use the "alt
" attribute to specify a text equivalent for some
elements. In HTML 4, authors may provide equivalents (or portions of
equivalents) in attribute values (e.g., the "summary" attribute for the
TABLE
element), in element content (e.g., OBJECT
for
external content it specifies, NOFRAMES
for frame equivalents, and
NOSCRIPT
for script equivalents), and in prose. Please consult the
Web Content Accessibility Guidelines 1.0 [WCAG10] and its associated
Techniques document [WCAG10-TECHS] for more
information about equivalents.
- Events and
scripting, event handler
- User agents often perform a task when an event occurs that
is due to user interaction (e.g., document loading, mouse motion or a key
press), a request from the
operating environment, etc. Some markup languages allow authors to
specify that a script, called an event handler, be executed when
the event occurs. An event handler is "explicitly associated with an
element" when the event handler is associated with that element
through markup or the DOM. The term "event
bubbling" describes a programming style where a single event
handler dispatches events to more than one element. In this case, the event
handlers are not explicitly associated with the elements receiving the events
(except for the single element that dispatches the events).
Note: The combination of HTML, style sheets, the Document
Object Model (DOM) and scripting is commonly referred to as
"Dynamic HTML" or DHTML. However, as there is no W3C specification that
formally defines DHTML, this document only refers to event handlers and
scripts.
-
Explicit user request
- In this document, the term "explicit user request" refers to any user
interaction with a control of
the user
agent user interface (not those in content), the focus, or
selection. Control behavior should be
documented.
Some examples of explicit user requests include when the user selects "New
viewport", responds "Yes" to a prompt in the user agent's user interface,
configures the user agent to behave in a certain way, or changes the selection
or focus with the keyboard or pointing device.
Note: Users make mistakes. For example, a user may
inadvertently respond "yes" to a prompt when they meant "no." In this document,
this type of mistake is still considered an explicit user request.
- Fee link
- For the purpose of this document, the term "fee link"
refers to a link that when activated, debits the user's electronic "wallet"
(generally, a "micropayment"). The link's role as a fee link is identified
through markup (in a manner that the user agent can
recognize). This definition of fee link excludes payment mechanisms
(e.g., some form-based credit card transactions) that cannot be recognized by
the user agent as causing payments. For more information about fee links, refer
to "Common Markup for micropayment per-fee-links"
[MICROPAYMENT].
-
Focus,
content focus,
user interface focus, current focus
- In this document, the term "content focus" refers to a
user agent mechanism that satisfies all of the following properties:
- It designates zero or one element in content
that is either
enabled or
disabled. (In general, the focus should only designate enabled
elements, but it may also designate disabled elements.)
- The user may "set" content focus (programmatically or through the user
interface) on an enabled element without triggering the associated
behaviors.
- It has state. The user may prefer to always move the content focus manually
from one element to another.
- It may be used (programmatically or through the user interface) to trigger
the behaviors associated with an enabled element. This is generally implemented
by making the focus respond to input device events (often just keyboard
events).
User interface mechanisms may resemble content focus, but do not satisfy all
of the properties. For example, text editors often implement a "caret" that
indicates the current location of text input or editing. The caret may have
state and may respond to input device events, but it does not enable users to
activate the behaviors associated with enabled elements.
The user interface focus shares the properties of the content focus except
the first: the user interface focus designates zero or one control of the user agent user interface that has associated
behaviors (e.g., radio button, text box, menu, etc.).
On the screen, the content focus may be
highlighted using colors, fonts, graphics, magnification, etc. The
content focus may also be highlighted when rendered as speech, for example
through changes in speech prosody. The dimensions of the rendered content focus
may exceed those of the viewport.
In this document, each viewport is expected to have at most one content
focus and at most one user interface focus. This document includes requirements
for content focus only, for user interface focus only, and for both. When a
requirement refers to both, the term "focus" is used.
When several viewports
coexist, at most one viewport's content focus or user
interface focus responds to input events; this is called the current focus.
-
Graphical
- In this document, the term "graphical" refers to
information (text, colors, graphics, images, animations, etc.) rendered for
visual consumption.
- Highlight
- In this document, "to highlight" means to emphasize
through the user interface. For example, user agents highlight which content is
selected or focused. Graphical highlight mechanisms include dotted boxes,
underlining, and reverse video. Synthesized speech highlight mechanisms include
alterations of voice pitch and volume.
- Input configuration
- An input configuration is the mapping of user agent
functionalities to some user
interface input mechanisms (e.g., menus, buttons, keyboard keys,
voice commands, etc.). The default input configuration is the mapping the user
finds after installation of the software; it must be documented (per checkpoint 12.3]). Input
configurations may be affected by author-specified bindings (e.g., through the
"accesskey" attribute of HTML 4 [HTML4]).
- Interactive element,
non-interactive element,
- An interactive element is piece of content that, by
specification, may have associated behaviors to be executed or carried out as a
result of user or programmatic interaction. For instance, the interactive
elements of HTML 4 [HTML4] include: links, image maps,
form elements, elements with a value for the "longdesc" attribute, and elements
with event
handlers explicitly associated with them (e.g., through the various
"on" attributes). The role of an element as an interactive element is subject
to
applicability . A non-interactive element is an element that, by
specification, does not have associated behaviors. The expectation of this
document is that interactive elements become enabled elements in some sessions, and
non-interactive elements never become enabled elements.
- Natural language
- Natural language is spoken, written, or signed human
language such as French, Japanese, and American Sign Language. On the Web, the
natural language of content may
be specified by markup or HTTP headers. Some examples include the
"lang" attribute in HTML 4 ([HTML4] section 8.1), the "xml:lang"
attribute in XML 1.0 ([XML], section 2.12), the
HTML 4 "hreflang" attribute for links in HTML 4
([HTML4],
section 12.1.5), the HTTP Content-Language header ([RFC2616], section 14.12) and the
Accept-Language request header ([RFC2616], section 14.4). See also
the definition of script.
-
Normative,
informative
- As used in this document, the term "normative" refers to
"that on which the requirements of this document depend for their most precise
statement." What is normative is required for conformance
(though the conformance scheme of this document allows claimants to exempt
certain normative provisions as long as the claim discloses the exemption).
What is identified as "informative" (sometimes, "non-normative") is never
required for conformance.
- Operating
environment
- The term "operating environment" refers to the environment
that governs the user agent's operation, whether it is an operating system or a
programming language environment such as Java.
-
Override
- In this document, the term "override" means that one
configuration or behavior preference prevails over another. Generally, the
requirements of this document involve user preferences prevailing over author
preferences and user agent default settings and behaviors. Preferences may be
multi-valued in general (e.g., the user prefers blue over red or yellow), and
include the special case of two values (e.g., turn on or off blinking text
content).
- Placeholder
- A placeholder is content generated by the user agent to
replace author-supplied content. A placeholder may be generated as the result
of a user preference (e.g., to not render images) or as
repair content (e.g., when an image
cannot be found). Placeholders can be any type of content, including text and
images.
This document includes requirements that the user be able to view the
original author-supplied content associated with a placeholder. To satisfy
these requirements, the user agent might render the content in place of the
placeholder or in a separate viewport (leaving the placeholder as is). A
request to view the original content associated with a placeholder is considered an explicit
user request to render that content.
This document does not require user agents to include placeholders in the document
object. A placeholder that is inserted in the document object should
conform to the Web Content Accessibility Guidelines 1.0 [WCAG10]. If a
placeholder is not part of the document object, it is part of the user
interface only (and subject, for example, to checkpoint 1.3).
-
Plug-in
- A plug-in is a program runs as part of the user agent and
it is not part of content.
Users generally choose to include or exclude plug-ins from their user
agent.
-
Point of regard
- The point of regard is a position in rendered
content that the user is presumed to be viewing. The dimensions of
the point of regard may vary. For example, it may be a point (e.g., a moment in
an audio rendering or a cursor in a graphical rendering), or a range of text
(e.g., focused text), or a two-dimensional area (e.g., content rendered through
a two-dimensional graphical viewport). The point of regard is almost always
within a viewport (though the dimensions of the point of regard could exceed
those of the viewport). The point of regard may also refer to a particular
moment in time for content that changes over time (e.g., an
audio-only presentation). User agents may determine the point of
regard in a number of ways, including based on viewport position in content,
content focus,
selection, etc. A user agent should not change the point of regard
unexpectedly as this may disorient the user.
-
Profile
- A profile is a named and persistent representation of user preferences that
may be used to configure a user agent. Preferences include input
configurations, style preferences, natural language preferences, etc. In
operating environments with distinct user accounts, profiles enable
users to reconfigure software quickly when they log on, and profiles may be
shared by several users. Platform-independent profiles are useful for those who
use the same user agent on different platforms.
-
Prompt
- In this document, "to prompt" means to require input from
the user. The user agent should allow users to
configure how they wish to be prompted. For instance, for a user
agent functionality X, configurations might include: always do X without
prompting me, never do X without prompting me, never do X but tell me when you
could have, never do X and never tell me that you could have, etc.
- Properties, values, and
defaults
- A user agent renders a document by applying formatting
algorithms and style information to the document's elements. Formatting depends
on a number of factors, including where the document is rendered: on screen, on
paper, through loudspeakers, on a braille display, on a mobile device, etc.
Style information (e.g., fonts, colors, speech prosody, etc.) may come from the
elements themselves (e.g., certain font and phrase elements in HTML), from
style sheets, or from user agent settings. For the purposes of these
guidelines, each formatting or style option is governed by a property and each
property may take one value from a set of legal values. Generally in this
document, the term "property"
has the meaning defined in CSS 2 ([CSS2], section 3). A reference to
"styles" in this document means a set of style-related properties.
- The value given to a property by a user agent when it is
installed is called the property's default value.
- Recognize
- Authors encode information in markup languages, style
sheet languages, scripting languages, protocols, etc. When the information is
encoded in a manner that allows the user agent to process it with certainty,
the user agent can "recognize" the information. For instance, HTML allows
authors to specify a heading with the H1 element, so a user agent that
implements HTML can recognize that content as a heading. If the author creates
headings using a visual effect alone (e.g., by increasing the font size), then
the author has encoded the heading in a manner that does not allow the user
agent to recognize it as a heading.
Some requirements of this document depend on content roles, content
relationships, timing relationships, and other information supplied by the
author. These requirements only apply when
the author has encoded that information in a manner that the user agent can
recognize. See the section on conformance
in User Agent Accessibility Guidelines 1.0 [UAAG10] for more information about
applicability.
In practice, user agents will rely heavily on information that the author
has encoded in a markup language or style sheet language. On the other hand,
behaviors, style, meaning encoded in a script, and
markup in an unfamiliar XML namespace may not be recognized by the user agent
as easily or at all.
-
Rendered content, rendered text
- Rendered content is the part of
content that the user agent makes available to the user's senses of
sight and hearing (and only those senses for the purposes of this document).
Any content that causes an effect that may be perceived through these senses
constitutes rendered content. This includes text characters, images, style
sheets, scripts, and anything else in content that, once processed, may be
perceived through sight and hearing.
The term "rendered text" refers to text content
that is rendered in a way that communicates information about the characters
themselves, whether visually or as speech.
- In the context of this document, "invisible content" is
content that influences graphical rendering of other content but is not
rendered itself. Similarly, "silent content" is content that
influences audio rendering of other content but is not rendered itself. Neither
invisible nor silent content is considered rendered content.
-
Repair content, repair text
- In this document, the term "repair content" refers to
content generated by the user agent in order to correct an error condition.
"Repair text" means repair content consisting only of
text. Some error conditions that may lead to the generation of
repair content include:
- Erroneous or incomplete content (e.g., ill-formed markup, invalid markup,
missing
conditional content that is required by specification, etc.);
- Missing resources for handling or rendering content (e.g., the user agent
lacks a font family to display some characters, the user agent doesn't
implement a particular scripting language, etc.);
This document does not require user agents to include repair content in the
document
object. Repair content inserted in the document object should
conform to the Web Content Accessibility Guidelines 1.0 [WCAG10]. For
more information about repair techniques for Web content and software, refer to
"Techniques for Authoring Tool Accessibility Guidelines 1.0"
[ATAG10-TECHS].
- Script
- In this document, the term "script" almost always refers to a scripting
(programming) language used to create dynamic Web content. However, in
checkpoints referring to the written (natural) language of content, the term
"script" is used as in Unicode [UNICODE] to mean "A collection of
symbols used to represent textual information in one or more writing systems."
Information encoded in scripts may be difficult for a user agent to recognize For instance, a user agent is not
expected to recognize that, when executed, a script will calculate a factorial.
The user agent will be able to recognize some information in a script by virtue
of implementing the scripting language or a known program library (e.g., the
user agent is expected to recognize when a script will open a viewport or
retrieve a resource from the Web).
- Selection, current
selection
- In this document, the term "selection" refers to a user
agent mechanism for identifying a range of
content (e.g., text, images, etc.). Generally, user agents limit
selection to text content (e.g., one or more fragments of text). The selection may be structured (based on the
document tree) or unstructured (e.g., text-based). The range may be empty.
On the screen, the selection may be
highlighted using colors, fonts, graphics, magnification, etc. The
selection may also be highlighted when rendered as speech, for example through
changes in speech prosody. The dimensions of the rendered selection may exceed
those of the viewport.
The selection may be used for a variety of purposes: for cut and paste
operations, to designate a specific element in a document for the purposes of a
query, as an indication of point of
regard, etc.
The selection has state. It may be set programmatically or through the user
interface.
In this document, each viewport is expected to have at most one selection.
When several viewports
coexist, at most one viewport's selection responds to input events; this is
called the current selection.
See the section on the selection
label for information about implementing a selection and
conformance.
Note: Some user agents may also implement a selection for
designating a range of information in controls of the user agent user interface. The current document
only includes requirements for a content
selection mechanism.
- Support, implement, conform
- In this document, the terms "support", "implement", and
"conform" all refer to what a developer has designed a user agent to do, but
they represent different degrees of specificity. A user agent "supports"
general classes of objects, such as "images" or "Japanese". A user agent
"implements" a specification (e.g., the PNG and SVG image format
specifications, a particular scripting language, etc.) or an
API (e.g., the DOM API) when it has been
programmed to follow all or part of a specification. A user agent "conforms to"
a specification when it implements the specification and satisfies its
conformance criteria. This document includes some conformance requirements to
other specifications (e.g., to a particular level of the "Web Content
Accessibility Guidelines 1.0" [WCAG10]).
- Synchronize
- In this document, "to synchronize" refers to the
time-coordination of two or more presentation components (e.g., in a multimedia
presentation, a visual
track with captions). For Web content developers, the requirement to
synchronize means to provide the data that will permit sensible
time-coordinated rendering by a user agent. For example, Web content developers
can ensure that the segments of caption text are neither too long nor too
short, and that they map to segments of the visual track that are appropriate
in length. For user agent developers, the requirement to synchronize means to
present the content in a sensible time-coordinated fashion under a wide range
of circumstances including technology constraints (e.g., small text-only
displays), user limitations (slow reading speeds, large font sizes, high need
for review or repeat functions), and content that is sub-optimal in terms of
accessibility.
- Text
- In this document, the term "text" used by itself refers to
a sequence of characters from a markup language's document character set. Refer to the "Character
Model for the World Wide Web " [CHARMOD] for more information
about text and characters. Note: This document makes use of
other terms that include the word "text" that have highly specialized meanings:
collated text transcript, non-text content,
text content, non-text
element, text
element, text
equivalent, and text
transcript.
-
Text content, non-text content, text
element, non-text element, text equivalent non-text
equivalent
- As used in this document a "text element" adds text characters to either content or the
user interface. Both in the Web Content Accessibility Guidelines 1.0
[WCAG10] and in this document, text elements are presumed to produce
text that can be understood when rendered visually, as speech, or as Braille.
Such text elements benefit at least these three groups of users:
- visually-displayed text benefits users who are deaf and adept in reading
visually-displayed text;
- synthesized speech benefits users who are blind and adept in use of
synthesized speech;
- braille benefits users who are deaf-blind and adept at reading
braille.
A text element may consist of both text and non-text data. For instance, a
text element may contain markup for style (e.g., font size or color), structure
(e.g., heading levels), and other semantics. The essential function of the text
element should be retained even if style information happens to be lost in
rendering.
A user agent may have to process a text element in order to have access to
the text characters. For instance, a text element may consist of markup, it may
be encrypted or compressed, or it may include embedded text in a binary format
(e.g., JPEG).
"Text content" is content that is composed of one or more text elements. A
"text equivalent" (whether in content or the user interface) is an
equivalent composed of one or more text elements. Authors generally
provide text equivalents for content by using the
conditional content mechanisms of a specification.
A "non-text element" is an element (in content or the user interface) that
does not have the qualities of a text element. "Non-text content" is composed
of one or more non-text elements. A "non-text equivalent" (whether in content
or the user interface) is an
equivalent composed of one or more non-text elements.
Note that the terms "text element" and "non-text element" are defined by the
characteristics of their output (e.g., rendering) rather than those of their
input (e.g., information sources) or their internals (e.g., format). Both text
elements and non-text elements should be understood as "pre-rendering" content
in contrast to the "post-rendering" content that they produce.
-
Text decoration
- In this document, a "text decoration" is any stylistic effect that the user
agent may apply to visually rendered
text that does not affect the layout of the document (i.e., does not
require reformatting when applied or removed). Text decoration mechanisms
include underline, overline, and strike-through.
-
Text transcript
- A text transcript is a text equivalent of audio
information (e.g., an
audio-only presentation or the
audio track of a movie or other animation). It provides text for
both spoken words and non-spoken sounds such as sound effects. Text transcripts
make audio information accessible to people who have hearing disabilities and
to people who cannot play the audio. Text transcripts are usually pre-written
but may be generated on the fly (e.g., by speech-to-text converters). See also
the definitions of captions
and
collated text transcripts.
- User
agent
- In this document, the term "user agent" is used in two
ways:
- Any software that retrieves and renders Web content for users. This may
include Web browsers, media players, plug-ins,
and other programs – including assistive technologies -- that help in
retrieving and rendering Web content.
- The subject of a conformance claim to User Agent Accessibility Guidelines
1.0
[UAAG10]. This is the most common use of the term in this document
and is the usage in the checkpoints.
- User agent default styles
- User agent default styles are style property values applied in the absence of
any author or user styles. Some markup languages specify a default rendering
for documents in that markup language. Other specifications may not specify
default styles. For example, XML 1.0 [XML] does not specify
default styles for XML documents. HTML 4 [HTML4] does not
specify default styles for HTML documents, but the CSS 2 [CSS2] specification
suggests a
sample default style sheet for HTML 4 based on current practice.
-
User interface
- For the purposes of this document, user interface includes
both:
- the "user agent user
interface", i.e., the controls (e.g., menus, buttons, prompts,
etc.) and mechanisms (e.g., selection and focus) provided by the user agent
("out of the box") that are not created by
content.
- the "content user interface", i.e., the enabled elements that are part of content, such
as form elements, links, applets,
etc.
The document distinguishes them only where required for clarity.
-
User styles
- User styles are style property values that come from user
interface settings, user style sheets, or other user interactions.
-
Visual-only presentation
- An visual-only presentation is content consisting
exclusively of one or more visual
tracks presented concurrently or in series. Examples of an
visual-only presentation include a silent movie.
-
Visual track
- A visual object is content rendered through a graphical viewport. Visual objects include graphics,
text, and visual portions of movies and other animations. An visual track is a
visual object that is intended as a whole or partial presentation. A visual
track does not necessarily correspond to a single physical object or software
object. A visual track may be text-based or graphic. A visual track may be
static or involve
animation.
-
Views,
viewports
- The user agent renders content through one or more viewports.
Viewports include windows, frames, pieces of paper, loudspeakers, virtual
magnifying glasses, etc. A viewport may contain another viewport (e.g., nested
frames). User interface controls such as prompts, menus, alerts, etc. are not
viewports.
When the dimensions (spatial or temporal) of a viewport exceed the
dimensions of rendered content (e.g., when the user can only view a portion of
a large document through a small graphical viewport, when audio content has
already been played, etc.), the user agent provides mechanisms such as scroll
bars and advance and rewind functionalities so that the user can access the
rendered content "outside" the viewport.
When several viewports
coexist, only one has the current
focus at a given moment. This viewport is
highlighted to make it stand out.
User agents may render the same content in a variety of ways; each rendering
is called a view. For
instance, a user agent may allow users to view an entire document or just a
list of the document's headers. These are two different views of the
document.
-
Voice browser
- From "Introduction and Overview of W3C Speech Interface Framework"
[VOICEBROWSER]: "A voice browser is a device (hardware and software)
that interprets voice markup languages to generate voice output, interpret
voice input, and possibly accept and produce other modalities of input and
output."
- Web resource
- The term "Web resource" is used in this document in
accordance with Web Characterization Terminology and Definitions Sheet [WEBCHAR] to
mean anything that can be identified by a Uniform Resource Identifier
(URI); refer to RFC 2396 [RFC2396].
For the latest version of any W3C specification please
consult the list of W3C Technical Reports at
http://www.w3.org/TR/. Some documents listed below may have been superseded
since the publication of this document.
Note: In this document, bracketed labels such as "[HTML4]"
link to the corresponding entries in this section. These labels are also
identified as references through markup.
There are two recommended ways to refer to the "Techniques for User Agent
Accessibility Guidelines 1.0" (and to W3C documents in general):
- References to a specific version of "Techniques for User Agent
Accessibility Guidelines 1.0". For example, use the "this version"
URI to refer to the current document:
http://www.w3.org/TR/2001/WD-UAAG10-TECHS-20010622/.
- References to the latest version of "Techniques for User Agent
Accessibility Guidelines 1.0". Use the "latest version" URI to refer to the
most recently published document in the series:
http://www.w3.org/TR/UAAG10-TECHS/.
In almost all cases, references (either by name or by link) should be to a
specific version of the document. W3C will make every effort to make this
document indefinitely available at its original address in its original form.
The top of this document includes the relevant catalog metadata for specific
references (including title, publication date, "this version"
URI, editors' names, and copyright information).
An XHTML 1.0
[XHTML10] paragraph including a reference to this specific document
might be written:
<p>
<cite><a href="http://www.w3.org/TR/2001/WD-UAAG10-TECHS-20010622/">
"Techniques for User Agent Accessibility Guidelines 1.0"</a></cite>,
I. Jacobs, J. Gunderson, E. Hansen, eds.,
W3C Working Draft, 22 June 2001.
The <a href="http://www.w3.org/TR/UAAG10-TECHS/">latest
version</a> of this document is available at
http://www.w3.org/TR/UAAG10-TECHS/.</p>
For very general references to this document (where stability of content,
anchors, etc., is not required), it may be appropriate to refer to the latest
version of this document. In this case, please use the "latest version" URI at
the top of this document.
- [DOM2CORE]
-
"Document Object Model (DOM) Level 2 Core Specification", A. Le
Hors, P. Le Hégaret, L. Wood, G. Nicol, J. Robie, M. Champion, S. Byrne,
eds., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113/.
- [DOM2STYLE]
-
"Document Object Model (DOM) Level 2 Style Specification", V.
Apparao, P. Le Hégaret, C. Wilson, eds., 13 November 2000. This W3C
Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/.
- [RFC2046]
- "Multipurpose Internet
Mail Extensions (MIME) Part Two: Media Types", N. Freed, N.
Borenstein, November 1996.
- [UAAG10]
- "User Agent Accessibility
Guidelines 1.0", I. Jacobs, J. Gunderson, E. Hansen, eds. The latest
draft of the guidelines is available at http://www.w3.org/TR/UAAG10/.
- [WCAG10]
- "Web
Content Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden,
and I. Jacobs, eds., 5 May 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/.
Some of the references in this section become normative if they are used to
satisfy the requirements of
guideline 6 and
guideline 8.
- [AT1998]
- The Assistive
Technology Act of 1998, 13 November 1998, United States P.L.
105-394.
- [ATAG10]
- "Authoring
Tool Accessibility Guidelines 1.0", J. Treviranus, C.
McCathieNevile, I. Jacobs, and J. Richards, eds., 3 February 2000. This W3C
Recommendation is http://www.w3.org/TR/2000/REC-ATAG10-20000203/.
-
[ATAG10-TECHS]
-
"Techniques for Authoring Tool Accessibility Guidelines 1.0", J.
Treviranus, C. McCathieNevile, I. Jacobs, and J. Richards, eds., 4 May 2000.
This W3C Note is http://www.w3.org/TR/2000/NOTE-ATAG10-TECHS-20000504/.
- [CHARMOD]
- "Character
Model for the World Wide Web", M. Dürst and F. Yergeau, eds.,
29 November 1999. This W3C Working Draft is
http://www.w3.org/TR/1999/WD-charmod-19991129/
- [CSS-ACCESS]
-
"Accessibility Features of CSS", I. Jacobs, J. Brewer, 4 August
1999. This W3C Note is http://www.w3.org/1999/08/NOTE-CSS-access-19990804.
- [CSS1]
- "CSS, level 1
Recommendation", B. Bos, H. Wium Lie, eds., 17 December 1996,
revised 11 January 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/REC-CSS1-19990111.
- [CSS2]
- "CSS, level 2
Recommendation", B. Bos, H. Wium Lie, C. Lilley, and I. Jacobs,
eds., 12 May 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-CSS2-19980512/.
- [DOM2EVENTS]
-
Document Object Model (DOM) Level 2 Events Specification, V. Pixley,
ed., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Events-20001113/.
- [DOM2RANGE]
-
Document Object Model (DOM) Level 2 Traversal and Range
Specification, J. Kesselman, J. Robie, M. Champion, P. Sharpe, V.
Apparao, and L. Wood, eds., 13 November 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-DOM-Level-2-Traversal-Range-20001113/.
- [HTML4]
- "HTML 4.01
Recommendation", D. Raggett, A. Le Hors, and I. Jacobs, eds., 24
December 1999. This W3C Recommendation is
http://www.w3.org/TR/1999/REC-html401-19991224/.
- [MATHML20]
-
"Mathematical Markup Language (MathML) Version 2.0", D. Carlisle, P.
Ion, R. Miner, N. Poppelier, et al., 21 February 2001. This W3C Recommendation
is http://www.w3.org/TR/2001/REC-MathML2-20010221/.
-
[MICROPAYMENT]
-
"Common Markup for micropayment per-fee-links", T. Michel, ed., 25
August 1999. This W3C Working Draft is
http://www.w3.org/TR/1999/WD-Micropayment-Markup-19990825/.
- [PNG]
- "PNG
(Portable Network Graphics) Specification 1.0", T. Boutell, ed., 1
October 1996. This W3C Recommendation is http://www.w3.org/TR/REC-png.
-
[PWD-USE-WEB]
- The How People
with Disabilities Use the Web, J. Brewer. This document provides an
introduction to use of the Web by people with disabilities. It is not yet a
formal W3C Working Draft.
- [RFC2396]
- "Uniform Resource
Identifiers (URI): Generic Syntax", T. Berners-Lee, R. Fielding, L.
Masinter, August 1998.
- [RFC2616]
- "Hypertext Transfer
Protocol -- HTTP/1.1", J. Gettys, J. Mogul, H. Frystyk, L. Masinter,
P. Leach, T. Berners-Lee, June 1999.
- [SMIL]
- "Synchronized
Multimedia Integration Language (SMIL) 1.0 Specification", P.
Hoschka, ed., 15 June 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-smil-19980615/.
-
[SMIL-ACCESS]
-
"Accessibility Features of SMIL", M-R. Koivunen, I. Jacobs, 21
September 1999. This W3C Note is
http://www.w3.org/TR/1999/NOTE-SMIL-access-19990921/.
- [SMIL20]
- Synchronized
Multimedia Integration Language (SMIL 2.0) Specification, J. Ayars,
et al., eds., 1 March 2001. This W3C Working Draft is
http://www.w3.org/TR/2001/WD-smil20-20010301/. The latest version of SMIL 2.0
is available at http://www.w3.org/TR/smil20.
- [SVG]
- "Scalable Vector
Graphics (SVG) 1.0 Specification", J. Ferraiolo, ed., 2 August 2000.
This W3C Candidate Recommendation is
http://www.w3.org/TR/2000/CR-SVG-20000802/.
- [SVG-ACCESS]
-
"Accessibility Features of SVG", C. McCathieNevile and M.-R.
Koivunen, 7 August 2000. This W3C Note is
http://www.w3.org/TR/2000/NOTE-SVG-access-20000807/.
- [UNICODE]
- "The Unicode
Standard, Version 3.1". This technical report of the Unicode Consortium is available at
http://www.unicode.org/unicode/reports/tr27/. This is a revision of "The
Unicode Standard, Version 3.0", The Unicode Consortium, Addison-Wesley
Developers Press, 2000. ISBN 0-201-61633-5. Refer also to
http://www.unicode.org/unicode/standard/versions/. For information about character
encodings, refer to Unicode Technical
Report #17 "Character Encoding Model".
-
[VOICEBROWSER]
- "Voice
Browsers: An introduction and glossary for the requirements drafts",
M. Robin, J. Larson, 23 December 1999. This document is
http://www.w3.org/TR/1999/WD-voice-intro-19991223/. This document includes
references to additional W3C specifications about voice browser
technology.
-
[WCAG10-TECHS]
-
"Techniques for Web Content Accessibility Guidelines 1.0", W.
Chisholm, G. Vanderheiden, and I. Jacobs, eds. This W3C Note is
http://www.w3.org/TR/1999/WAI-WEBCONTENT-TECHS-19990505/.
- [WEBCHAR]
- "Web
Characterization Terminology and Definitions Sheet", B. Lavoie, H.
F. Nielsen, eds., 24 May 1999. This is a W3C Working Draft that defines some
terms to establish a common understanding about key Web concepts. This W3C
Working Draft is http://www.w3.org/1999/05/WCA-terms/01.
- [XHTML10]
- "XHTML[tm]
1.0: The Extensible HyperText Markup Language", S. Pemberton, et
al., 26 January 2000. This W3C Recommendation is
http://www.w3.org/TR/2000/REC-xhtml1-20000126/.
- [XLINK]
- "XML Linking
Language (XLink) Version 1.0", S. DeRose, E. Maler, D. Orchard, B.
Trafford, eds., 3 July 2000. This XML 1.0 Candidate Recommendation is
http://www.w3.org/TR/2000/CR-xlink-20000703/.
- [XML]
- "Extensible
Markup Language (XML) 1.0", T. Bray, J. Paoli, C.M.
Sperberg-McQueen, eds., 10 February 1998. This W3C Recommendation is
http://www.w3.org/TR/1998/REC-xml-19980210.
- [XMLSTYLE]
-
"Associating Style Sheets with XML documents Version 1.0", J. Clark,
ed., 29 June 1999. This W3C Recommendation is
http://www.w3.org/1999/06/REC-xml-stylesheet-19990629/
- [XSLT]
- "XSL
Transformations (XSLT) Version 1.0", J. Clark, 16 November 1999.
This W3C Recommendation is http://www.w3.org/TR/1999/REC-xslt-19991116.
Note: W3C does not guarantee the stability of any of
the following references outside of its control. These references are included
for convenience. References to products are not endorsements of those products
by W3C.
- [APPLE-HI]
- Refer to the following guidelines from Apple:
- [BHO]
- Browser
Helper Objects: The Browser the Way You Want It, D. Esposito,
January 1999. Refer also to
http://support.microsoft.com/support/kb/articles/Q179/2/30.asp.
- [ED-DEPT]
-
"Requirements for Accessible Software Design", US Department of
Education, version 1.1 March 6, 1997.
- [EITAAC]
-
"EITAAC Desktop Software standards", Electronic Information
Technology Access Advisory (EITAAC) Committee.
- [IBM-ACCESS]
- "Software
Accessibility", IBM Special Needs Systems.. Refer to the IBM guidelines for
software accessibility, IBM guidelines for Java
accessibility.
- [ICCCM]
- "The Inter-Client
communication conventions manual". A protocol for communication
between clients in the X Window system.
- [ICE-RAP]
- "An
ICE Rendezvous Mechanism for X Window System Clients", W. Walker. A
description of how to use the ICE and RAP protocols for X Window clients.
-
[JAVA-ACCESS]
- "IBM Guidelines for
Writing Accessible Applications Using 100% Pure Java", R.
Schwerdtfeger, IBM Special Needs Systems.
-
[JAVA-CHECKLIST]
- "Java
Accessibility Guidelines and Checklist". IBM Special Needs
Systems.
- [JAVA-TUT]
- "The Java
Tutorial. Trail: Creating a GUI with JFC/Swing". An online tutorial
that describes how to use the Swing Java Foundation Class to build an
accessible user interface. Refer also to information on the Java Foundation Classes.
- [JAVA13]
- Refer to information about
character encodings required by Java version 1.3.
- [JAVAAPI]
- Information on Java Accessibility API can be found at Java Accessibility
Utilities.
- [MOTIF]
- The
OSF/Motif Style Guide.
- [MS-ENABLE]
-
Software accessibility guidelines for Windows applications. Refer also to
Built-in
accessibility features.
-
[MS-KEYBOARD]
- Information on keyboard
assistance for Internet Explorer and MS Windows.
-
[MS-SOFTWARE]
- "The
Microsoft Windows Guidelines for Accessible Software Design".
Note: This page summarizes the guidelines and includes links
to the full guidelines in various formats (including plain text).
- [MSAA]
- Information on active accessibility can be found at the Microsoft Active
Accessibility home page.
-
[NOTES-ACCESS]
- "Lotus Notes
Accessibility Guidelines" IBM Special Needs Systems.
- [PHOTO-RDF]
-
"Describing and retrieving photos using RDF and HTTP", Y. Lafon and
B. Bos. The 3 May 2000 version of the W3C Note is
http://www.w3.org/TR/2000/NOTE-photo-rdf-20000503/.
- [SAMI]
- Information on
Synchronized Accessible Multimedia Interchange (SAMI)
accessibility.
- [SUN-DESIGN]
- Articles, Talks, and
Papers from Sun Microsystems about accessibility.
- [SUN-HCI]
-
"Towards Accessible Human-Computer Interaction", Eric Bergman, Earl
Johnson, Sun Microsytems 1995. A substantial paper, with a valuable print
bibliography.
-
[TALKINGBOOKS]
- National Information Standards
Organization. One activity pursued by this organization concerns Digital Talking Books. Refer to the
"Digital Talking Book
Features List" and "Digital Talking Book
Standards Committee Document Navigation Features List" drafts for
more information.
- [TRACE-EZ]
- "EZ ACCESS(tm) for
electronic devices V 2.0 implementation guide", C. M. Law, G. C.
Vanderheiden, 23 February 2000. This guide, developed by the Trace Research and Development Center,
describes a simple set of interface enhancements that can be applied to
electronic devices so that they can be used by people with disabilities, or
anyone who experiences difficulty using a device in the standard method of
operation.
- [TRACE-REF]
- "Application
Software Design Guidelines" compiled by G. Vanderheiden. A thorough
reference work.
- [WHAT-IS]
- "What is Accessible Software", James W. Thatcher, Ph.D., IBM,
1997. This paper, available at the IBM
Accessibility Center, gives a short example-based introduction to the
difference between software that is accessible, and software that can be used
by some assistive technologies.
-
[XGUIDELINES]
- Information on accessibility
guidelines for Unix and X Window applications. The Open Group has various guides that
explain the Motif and Common Desktop Environment (CDE) with
topics like how users interact with Motif/CDE applications and how to customize
these environments. Note: In X, the terms client and server
are used differently from their use when discussing the Web.
A list of alternative
Web browsers (assistive technologies and other user agents designed for
accessibility) is maintained at the WAI Web site.
- [ADOBE]
- access.adobe.com. Tools
and information about Adobe PDF and accessibility.
- [ALTIFIER]
- The Altifier
Tool generates "alt" text intelligently.
- [AMAYA]
- Amaya is W3C's test-bed browser and
editor.
- [AWB]
- The Accessible Web Browser<, senior project at the University of Illinois Champaign-Urbana
-
[CSSVALIDATOR]
- W3C's CSS Validator
service.
- [DIRECTDOM]
- DirectDom technology, available from alphaWorks, allows a Java developer
to manipulate the live Document Object Model of a browser or Scalable Vector
Graphics plugin to build rich graphical user interfaces.
- [G2]
- The G2 player version 7 for Windows.
- [HELPDB]
- HelpDB is a test tool
for Web table navigation.
- [HPR]
- Home Page Reader.
- [IE-WIN]
- Internet Explorer 5.0 for
Windows 95, Windows 98, and Windows NT. Refer also to information on using COM with
IE. Refer also to
information about monitoring HTML events in the IE document
object model.
- [JFW]
- JAWS for Windows.
- [LYNX]
- The Lynx Browser.
- [MOZILLA]
- The Mozilla browser.
- [NAVIGATOR]
- Netscape
Navigator.
- [ODP-DOM]
- Open
Directory Project information on the W3C DOM.
- [OPERA]
- The Opera Browser.
- [QUICKTIME]
- The QuickTime player.
- [TABLENAV]
- A
table navigation script from the Trace Research Center.
- [VALIDATOR]
- W3C's HTML/XML Validator
service.
- [VIAVOICE]
- ViaVoice speech
recognition software.
- [WINDOWEYES]
- Window-Eyes.
- [WINVISION]
- Winvision.
-
[BRAILLEFORMATS]
- "Braille Formats: Principles of
Print to Braille Transcription 1997" .
- [NBA]
- The National Braille
Association.
- [NBP]
- The National Braille Press.
- [RFBD]
- Recording for the Blind and
Dyslexic.
- [SAPI]
- Microsoft's Speech Application
Programming Interface.
-
[SPEAK2WRITE]
- Speak to Write is a site about
using speech recognition to promote accessibility.
- [ISO639]
- "Codes for the representation of names of languages", ISO 639:1988. For
more information, consult
http://www.iso.ch/cate/d4766.html. Refer also to
http://www.oasis-open.org/cover/iso639a.html.
The active participants of the User Agent Accessibility Guidelines Working
Group who authored this document were: James Allan, Denis Anson (College
Misericordia), Harvey Bingham, Al Gilman, Jon Gunderson (Chair of the Working
Group, University of Illinois, Urbana-Champaign), Eric Hansen (Educational
Testing Service), Ian Jacobs (Team Contact, W3C), Tim Lacy (Microsoft), Charles
McCathieNevile (W3C), David Poehlman, Mickey Quenzer, Gregory Rosmaita
(Visually Impaired Computer Users Group of New York City), and Rich
Schwerdtfeger (IBM).
Many thanks to the following people who have contributed through review and
past participation in the Working Group: Paul Adelson, Kitch Barnicle, Olivier
Borius, Judy Brewer, Dick Brown, Bryan Campbell, Kevin Carey, Tantek
Çelik, Wendy Chisholm, David Clark, Chetz Colwell, Wilson Craig, Nir
Dagan, Daniel Dardailler, B. K. Delong, Neal Ewers, Geoff Freed, John Gardner,
Larry Goldberg, Glen Gordon, John Grotting, Markku Hakkinen, Earle Harrison,
Chris Hasser, Kathy Hewitt, Philipp Hoschka, Masayasu Ishikawa, Phill Jenkins,
Earl Johnson, Jan Kärrman (for help with html2ps), Leonard Kasday,
George Kerscher, Marja-Riitta Koivunen, Peter Korn, Josh Krieger, Catherine
Laws, Aaron Leventhal, Greg Lowney, Susan Lesch, Scott Luebking, William
Loughborough, Napoleon Maou, Peter Meijer, Karen Moses, Masafumi Nakane, Mark
Novak, Charles Oppermann, Mike Paciello, David Pawson, Michael Pederson, Helen
Petrie, Michael Pieper, Richard Premack, Jan Richards, Hans Riesebos, Joe
Roeder, Lakespur L. Roca, Madeleine Rothberg, Lloyd Rutledge, Liam Quinn, T.V.
Raman, Robert Savellis, Constantine Stephanidis, Jim Thatcher, Jutta
Treviranus, Claus Thogersen, Steve Tyler, Gregg Vanderheiden, Jaap van
Lelieveld, Jon S. von Tetzchner, Willie Walker, Ben Weiss, Evan Wies, Chris
Wilson, Henk Wittingen, and Tom Wlodkowski.