Techniques for User Agent Accessibility Guidelines 1.0
W3C Working Draft 29 December 2000
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- Editors:
- Ian Jacobs, W3C
Jon Gunderson, University of Illinois at
Urbana-Champaign
Eric Hansen, Educational Testing
Service
- Authors and Contributors:
- See acknowledgements.
Copyright
©1999 - 2000 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 cover 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).
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 29 December 2000 Working Draft of Techniques for User Agent
Accessibility Guidelines 1.0, for review by W3C Members and other interested
parties. 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.
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.
This document suggests some techniques for satisfying the requirements of
the "User Agent Accessibility Guidelines 1.0" [UAAG10]. 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 lists each checkpoint of "Techniques for 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 "Techniques for User Agent Accessibility Guidelines
1.0". Each checkpoint definition is followed by a list of techniques,
information about related resources, and references to the accessibility topics
in section 3. The accessibility topics of section 3 apply to more than one
checkpoint.
Note: Most of the techniques in this document are designed
for mainstream (graphical) browsers and multimedia players. 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]
- 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]
- 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]
- 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
"Techniques for User Agent Accessibility Guidelines 1.0" [UAAG10], please
refer to that document.
Checkpoints for communication with other software:
-
1.1 Ensure that the user may operate the user agent fully with
keyboard input alone, pointing device input alone, and voice input alone. [Priority 1] (Checkpoint
1.1)
-
Techniques:
-
Since the subject of a claim may be one or more software components, one
could, for example, claim conformance for the following software used
together:
- a browser that doesn't support character input through the mouse
- an on-screen keyboard, operable through a pointing device, that
communicates with the browser through a keyboard API.
Functionalities addressed by this checkpoint include the following:
-
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 must also be able to do so
through the keyboard and other supported devices. Other operations include cut,
copy, and paste.
- Set the
focus. Ensure that software may be
installed, uninstalled, and updated in a device-independent manner.
- Navigate content.
- Navigate links (see link techniques).
- Use the graphical user
interface menus.
- Fill out forms.
- Access documentation.
- Configure the software.
- Install, uninstall, and update the user agent software.
Ensure that people with disabilities are involved in the design and testing
of the software.
-
- 1.2
Implement the standard accessibility APIs of the operating system and supported
programming languages. Where these APIs do not enable the user agent to satisfy
the requirements of this document, use the
standard input and output APIs of the
operating system and supported programming languages.
[Priority 1] (Checkpoint
1.2)
- Note: Accessibility APIs enable
assistive technologies to monitor input and output events. As part of
satisfying this checkpoint, the user agent needs to ensure that text content is available as text through these
APIs (and not, for example, as a series of strokes drawn on the screen).
-
Techniques:
-
- Microsoft Active Accessibility ([MSAA]) is the standard accessibility
API for the Windows 95/98/NT operating systems.
- Sun Microsystems Java Accessibility API ([JAVAAPI]) in the Java JDK is the
standard accessibility API for the Java environment.
- Operating system and application frameworks provide standard mechanisms 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 standard mechanisms for receiving keyboard input in the case
of desktop operating systems. Should you use an application framework such as
the Microsoft Foundation Classes, the framework used must support the same
standard input mechanisms.
- Do not communicate directly with an input device; this may circumvent
system 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 standard input mechanisms for proper
application coexistence within the user interface framework.
- Do not implement your own input device event queue mechanism; this may
circumvent system messaging. Some assistive technologies use standard 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) is 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 system and application frameworks provide standard mechanisms for
using standard output devices. In the case of common desktop operating systems
such as Windows, OS/2, and Mac OS, standard APIs are provided for writing to the display
and the multimedia subsystems.
- Do not render 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 standard system
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 emphasizes access to the document
object model rather than a particular rendering. For instance,
instead of relying on system calls to draw text, assistive technologies should
access the text through the document object model.
- Common operating system 2D 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 system
sounds.
- When writing textual information in a GUI operating system, use standard
operating system APIs for drawing text.
- Use operating system 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 systems like Windows, a
set of standard audio sound resources are provided to support standard sounds
such as alerts. These preset sounds are used to
activate 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 active window. It is
important to use the standard mechanisms to generate audio feedback so that
operating system or special assistive technologies can add additional
functionality for users with hearing disabilities.
- Enhance the functionality of standard system controls to improve
accessibility where none is provided by responding to standard 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 standard keyboard activation facility for Abstract Window Toolkit
components.
-
- 1.3
Implement the operating system's
standard APIs for the keyboard. [Priority 1] (Checkpoint
1.3)
- Note: An operating system may define more than one
standard API for the keyboard. For instance, for Japanese and Chinese, input
may be processed in two stages, with an API for each. This checkpoint is an
important special case of
checkpoint 1.1. Refer
also to checkpoint 9.8.
-
Techniques:
-
- Apply the techniques for checkpoint 1.1 to the keyboard.
- Account for author-specified keyboard bindings, such as those specified by
"accesskey" attribute in HTML 4 ([HTML4], section
17.11.2).
- Allow the user to trigger event
handlers (e.g., mouseover, mouseout, click, etc.) from the
keyboard.
- 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.
-
Checkpoints for user interface accessibility:
-
1.4 Ensure that the user can interact with all
active elements in a
device-independent manner.
[Priority 1] (Checkpoint
1.4)
- Note: For example, users without a pointing device (such
as some users who are blind or have physical disabilities) must be able to activate form
controls and links (including the links in a client-side image
map).
-
Techniques:
-
- see checkpoint 1.1
and checkpoint 1.5.
- see image map techniques.
- In the "Document Object Model (DOM) Level 2 Events Specification" ([DOM2EVENTS]), all elements may
have associated behaviors. Assistive technologies should be able to activate
these elements through the DOM. For example, a DOM 'focusin' event may cause a
JavaScript function to construct a pull-down menu. Allowing programmatic
activation of this function will allow users to operate the menu through speech
input (which benefits users of voice browsers in addition to assistive
technology users). Note that, for a given element, the same event may trigger
more than one event handler, and assistive technologies must be able to
activate each of them. Descriptive information about handlers can allow
assistive technologies to select 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. Refer also to checkpoint
5.3.
-
- 1.5 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. [Priority 1] (Checkpoint
1.5)
- 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 5.4, a text equivalent for each such message must
be available through a standard API.
Refer also to checkpoint 5.5.
-
Techniques:
-
- Render text messages graphically on the status bar of the user interface.
Provide this information automatically and allow users to query the viewport
for it (e.g., through a menu or keyboard binding).
- For graphical user interface elements such as proportional scroll bars,
provide a text equivalent that conveys the proportion of the content viewed
(e.g., as a percentage) and that may be rendered graphically, as synthesized
speech, and as braille. For images that render gradually (coarsely to finely),
it is not necessary to show percentages for each rendering pass.
- For beeps or flashes provide a text
equivalent that can be rendered as braille, synthesized speech, or
graphically-rendered text.
- For user interface components that convey important information using
sound, also provide alternative, parallel graphical representation of the
information for 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. Provide braille renderings of text equivalents for deaf-blind users
who cannot use audio or graphical cues and who rely on braille.
- Allow users to configure when to render status information so that
assistive technologies may announce changes in status at appropriate times. For
instance, allow the user to hide the status bar in order to hide a text
rendering.
- 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 control group
(e.g., FIELDSET in HTML).
-
Checkpoints for content accessibility:
- 2.1 Make all
content available through the user interface. [Priority 1] (Checkpoint
2.1)
- Note: Users must have access to the
entire document
object through the user interface, including recognized
equivalents, attributes, style sheets, etc. This checkpoint does not
require that all content be available in every
viewport. A document
source view is an important part of a solution for providing access
to content, but is not a sufficient solution on its own for all content. see guideline 5 for more
information about programmatic access to content.
-
Techniques:
-
- Some users benefit from concurrent access to more than one
equivalent. 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. 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.
- When content changes dynamically (e.g., due to embedded scripts or content
refresh), users must have access to the content before and after the
change.
- Provide structured (not all at once) access to attribute values. 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 document source view.
- A document source view may be the most usable readily-achievable view for
some content such as embedded fragments of style and scripting languages.
- In general, user agent developers should not rely on "source view" for
conveying information to users, many of whom will not be familiar with markup
languages and for whom navigation may be difficult. However, since some content
may not be accessible to users otherwise, a source view may be useful as a
"last resort" view.
- See the section on access to content.
- See the section on link techniques.
- See the section on table techniques.
- See the section on frame techniques.
- See the section on form techniques.
- Sections 10.4 ("Client Error 4xx") and 10.5 ("Server Error 5xx") of the
HTTP/1.1 specification 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.
- 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 explicit expansion in one location, look for another
occurrence in content with an explicit expansion. User agents may also look for
possible expansions (e.g., in parentheses) in surrounding context, though that
is a less reliable repair.
-
- 2.2 For a presentation that requires
user input within a specified time interval, allow the user to configure the user agent to pause the
presentation automatically and await user input before proceeding. [Priority 1] (Checkpoint
2.2)
- Note: In this configuration, the user
agent may have to pause the presentation more than once, depending on the
number of times input is requested.
-
Techniques:
-
- As for other checkpoints, the user agent is not required to allow control
of content properties that it cannot
recognize. If timing effects are described through scripts in a
manner that the user agent can recognize, it must allow the user to control the
timing of the presentation.
- 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.
- Provide easy-to-use controls (including both mouse and keyboard commands)
to allow users to pause a presentation and advance and rewind by small or large
time increments. Note: When a user must respond to a link by
pausing the program and activating the link, the time dependent nature of the
link does not change since the user must respond somehow in the predetermined
time. The pause feature is only effective in conjunction with the ability to
rewind to the link, or when the pause can be configured to stop the
presentation automatically and require the user to respond before continuing,
either by responding to the user input or by continuing with the flow of the
document.
- Highlight the fact that there are active elements in a presentation and
allow users to navigate to and activate them. For example, indicate the
presence of active elements on the status bar and allow the user to navigate
among them with the keyboard or mouse.
- For additional control, user agents may allow users to slow the
presentation.
-
- 2.3 Provide easy access to each
equivalent and each equivalency
target through at least one of the following mechanisms: (1)
allowing configuration to render the equivalent instead of the equivalency
target; (2) allowing configuration to render the equivalent in addition to the
equivalency target; (3) allowing the user to select the equivalency target and
then inspect its equivalents; (4) providing a direct link to the equivalent in
content, just before or after the equivalency target in document order. [Priority 1] (Checkpoint
2.3)
- Note: For example, if an image in an
HTML document has text
equivalents, provide access to them (1) by replacing the image with
the rendered equivalents, (2) by rendering the equivalents near the image, (3)
by allowing the user to select the image and then inspect its equivalents, or
(4) by allowing the user to follow readily available links to the
equivalents.
-
Techniques:
-
- See the section on access to content.
- Allow users to choose more than one equivalent at a given time. For
instance, 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 mutually exclusively.
- In the user interface, construct a list of all available tracks from short
descriptions provided by the author (e.g., through the "title" attribute).
- Allow the user to configure different natural language preferences for different
types of equivalents (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 equivalent 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.
- Consider system level natural language preferences as the user's default
language preference. However, do not send HTTP Accept-Language request headers
([RFC2616], section 14.4) based on
the operating system 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 system defines one language, while the
Accept-Language request header may include many languages in different
priorities. Setting Accept-Language to be the operating system 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.
-
-
2.4 Allow the user to specify that text transcripts,
collated text transcripts, captions,
and auditory
descriptions be rendered at the same time as the associated audio
and visual tracks. [Priority 1] (Checkpoint
2.4)
-
Techniques:
-
- User agents that implement SMIL 1.0 ([SMIL]) should implement the
"Accessibility Features of SMIL" [SMIL-ACCESS]. In particular,
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 does not include a
mechanism equivalent to 'system-captions' for auditory descriptions. The next
version of SMIL is expected to include a test attribute for auditory
descriptions.
Another SMIL 1.0 test attribute, 'system-overdub-or-captions', allows users
to select 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 equivalents. The Apple QuickTime player currently
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 which play Microsoft Windows
Media Object presentations should enable people to turn on and off other
equivalents, including auditory description and alternative visual tracks.
- For other formats, at a minimum, users must be able to turn on and off
auditory descriptions and captions.
-
- 2.5 Respect author-specified
synchronization cues during rendering.
[Priority 1] (Checkpoint
2.5)
-
Techniques:
-
- 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 must 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.
- 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.
Captions are essential for individuals who require an alternative way of
accessing the meaning of audio, such as individuals who are deaf. 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 must
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 must determine how they will handle
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 clicking on a text equivalent (or some outline of it), then do all rendered
equivalents jump at the same time? Will one be able to return to one's previous
location (or undo the action)?
Developers of user agents must anticipate many of the challenges that may
arise in synchronization of diverse equivalents.
The term "synchronization cues" in checkpoint 2.5 refers to pieces of information that may
affect synchronization, such as the size and expected duration of equivalents
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),
user preferences, etc.
-
- 2.6 For non-text content that has no recognized text equivalent, allow configuration to
generate repair
text. If the non-text content is included by URI reference, base the
repair text on the URI reference and content type of the
Web resource. Otherwise, base the repair
text on the name of the element that includes the non-text
content. [Priority 2] (Checkpoint
2.6)
- Note: For information on URI references, refer to "Uniform
Resource Identifiers (URI): Generic Syntax" ([RFC2396], section 4). Some markup
languages (such as HTML 4 [HTML4] and SMIL 1.0 [SMIL] require the
author to provide text equivalents for some content. When they don't, the user
agent is required by this document to generate
repair text. Refer also to
checkpoint 2.7.
-
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.
- Text equivalents may come from markup, inside images (e.g., refer to
"Describing and retrieving photos using RDF and HTTP"
[PHOTO-RDF]), etc. User agents are expected to recognize equivalents
by specification See techniques for missing
equivalents.
- When configured to generate text, also inform the user (e.g., in the
generated text itself) that this content was not provided intentionally by the
author as a text equivalent.
- See content repair techniques
-
- 2.7 Allow configuration so that when the author
has specified an empty text
equivalent for non-text
content, the user agent generates no
repair text or generates repair text as required by checkpoint 2.6. [Priority 3] (Checkpoint
2.7)
- Note: An empty text equivalent (e.g.,
alt=""
)
is considered to be a valid text
equivalent in some authoring scenarios. For instance, when some non-text
content has no other function than pure decoration, or 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. Refer also to checkpoint 2.6.
-
Techniques:
-
- User agents should render nothing in this case because the author may
specify a null text equivalent for content that has no function in the page
other than as decoration. In this case, the user agent should not render
generic labels such as "[INLINE]" or "[GRAPHIC]".
- Allow the user to toggle the rendering of null text equivalents: between
nothing and an indicator of a null equivalent (e.g., an icon with the text
equivalent "EMPTY TEXT EQUIVALENT").
-
-
2.8 Allow the user to configure the user agent not to render content
in unsupported natural
languages. Indicate to the user in context that author-supplied
content has not been rendered. [Priority 3]
(Checkpoint
2.8)
- 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 only requires one
global setting, not configuration for specific natural languages.
-
Techniques:
-
- 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.
- CSS2's attribute selector may be used with the "lang" or "xml:lang"
attributes to control rendering based on author-supplied natural language
information.
- 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 "Korean text -- unable to read". 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.
- 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].
- See techniques for generated content,
which may be used to insert text to
indicate a language change.
- 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.
- Implement content negotiation so that users may specify language
preferences. Or allow the user to choose a
Web resource when several are available in different languages.
- There may be cases when a conforming user agent supports a natural language
but a speech synthesizer does not, or vice versa.
- See techniques for synthesized speech and
checkpoint 5.4.
- See content repair techniques
-
In addition to the techniques below, refer also to the section on user control of style.
Checkpoints for content accessibility:
-
3.1 Allow the user to configure
the user agent not to render background images. In this configuration, provide
an option to alert the user when a background image is available but has not
been rendered. [Priority 1] (Checkpoint
3.1)
- Note: 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". When background images are not rendered,
user agents should render a solid background color (see checkpoint 4.3). In this
configuration, the user agent is not required to retrieve background images
from the Web.
-
Techniques:
-
- Since background images may make it difficult or impossible to read
superimposed text, allow the user to turn off embedded or background images
through the user
agent user interface. Note that any equivalents for those images must still be
available.
- In CSS, background images may be turned on/off with the
'background' and 'background-image' properties ([CSS2], section 14.2.1).
- 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).
-
- 3.2
Allow the user to configure
the user agent not to render audio, video, or animated images except on
explicit request from the user. In this configuration, provide an option to
render a substitute placeholder in context for each unrendered source of audio,
video, or animated image. When placeholders are rendered, allow the user to
activate each placeholder individually and replace it with the original
author-supplied content. [Priority 1] (Checkpoint
3.2)
- Note: 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 that is not an explicit request (e.g., when the user activates a
link). Activation of a placeholder is considered an explicit user request to
render the original content. 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. Refer also
checkpoint 4.5, checkpoint 4.9 and checkpoint
4.10.
-
Techniques:
-
- User agent may satisfy this checkpoint by treating content as invisible or silent
(e.g., by implementing the
'visibility' property defined in section 11.2 of CSS 2 [CSS2]). However,
this solution means that the content is processed, though not rendered, and
processing may cause undesirable side effects such as triggering 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.
-
- 3.3
Allow the user to configure
the user agent to render animated or blinking text as motionless text. [Priority 1] (Checkpoint
3.3)
-
Techniques:
-
- 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). Render static text in place of blinking text.
- 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).
-
-
3.4 Allow the user to configure
the user agent to render blinking images as motionless images. [Priority 1] (Checkpoint
3.4)
-
Techniques:
-
- Use, for example, the first frame of the blinking image as the motionless
substitute.
- Allow the user to turn off the blinking image through the user
agent user interface (e.g., by pressing the Escape key to
stop animations).
-
- 3.5 Allow the user to configure the user agent not to execute scripts
or applets. In this configuration, provide an option to alert the user when
scripts or applets are available.
[Priority 1] (Checkpoint
3.5)
-
Techniques:
-
- Control of scripts is particularly important when they 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.
- 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.
- This checkpoint includes scripts that run on load and when other events
occur (e.g., user interface events).
- See the section on script techniques
-
-
3.6 Allow
configuration so that an author-specified "client-side redirect"
(i.e., one initiated by the user agent, not the server) does not change content except on explicit user request. Allow the user to access
the new content manually (e.g., by following a link).
[Priority 2] (Checkpoint
3.6)
-
Techniques:
-
- 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 Allow
configuration so that author-specified content refreshes do not
change
content except on explicit
user request. Allow the user to request the new content manually
(e.g., by activating a button or following a link). Alert the user, according
to the schedule specified by the author, whenever fresh content is available
(to be obtained on explicit user request).
[Priority 2] (Checkpoint
3.7)
-
Techniques:
-
- Alert the user of pages that refresh automatically and allow them to
specify a refresh rate through the user
agent user interface.
- Allow the user to slow content refresh to once per 10 minutes.
- 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.
-
- 3.8 Allow the user to configure the user agent not to render images.
[Priority 2] (Checkpoint
3.8)
-
Techniques:
-
- Provide a simple command that allows users through the user agent user interface to turn on/off the
rendering of images on a page. When images are turned off, render any
associated equivalents.
- 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 (content accessibility):
- 4.1
Allow the user to configure and
control the reference size of rendered text with an option to
override author-specified and user agent default sizes of rendered text. Make
available the range of system font sizes.
[Priority 1] (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). The default
reference size of rendered text may vary among user agents. User agents may
offer different mechanisms to allow the user to control the size of rendered
text, for example by allowing the user to change the font size or by allowing
the user to zoom or magnify content (refer, for example to the Scalable Vector
Graphics specification
[SVG]).
-
Techniques:
-
- 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.
- Inherit text size information from user preferences specified for the
operating system.
- 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).
- Use operating system magnification features.
- Implement the
'font-size' property in CSS ([CSS2], section 15.2.4).
- When scaling text, maintain size relationships among text of different
sizes.
- Allow users to configure link text to be
rendered so that users with physical disabilities using a mouse may easily
activate links. This may be done through style sheets, for example.
-
-
4.2 Allow the user to configure
the font family of all rendered text, with an option to override
author-specified, and user agent default, font families. Allow the user to
select from among the range of system font families.
[Priority 1] (Checkpoint
4.2)
- Note: For
text that cannot be rendered properly using the user's selected font
family, the user agent may select an alternative font family.
- Note: For example, allow the user to
specify that all
text must be rendered in a particular
sans-serif font family.
-
Techniques:
-
- Inherit font family information from user preferences specified for the
operating system.
- 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.
- 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
Allow the user to configure
the foreground and background color of all text, with an option to override
foreground and background colors specified by the author or user agent
defaults. Allow the user to select from among the range of system colors. [Priority 1] (Checkpoint
4.3)
-
Techniques:
-
- Inherit foreground and background color information from user preferences
specified for the operating system.
- 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).
- 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 (content accessibility):
- 4.4 Allow the user to slow the
presentation rate of audio, video and animations that are not recognized as style. 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.
[Priority 1] (Checkpoint
4.4)
- Refer also to checkpoint
2.5.
-
Techniques:
-
- Allowing the user to slow the presentation of video, animations, and audio
will benefit individuals with specific learning disabilities, cognitive
disabilities, or individuals with newly acquired sensory limitations (such as a
person who is newly blind and learning to use a screen reader). The same
feature will benefit individuals who have beginning familiarity with a natural
language.
- 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.
- When changing the rate of audio, avoid pitch distortion.
- Some formats do not allow changes in playback rate.
-
- 4.5 Allow the user to stop, pause,
resume, fast advance, and fast reverse audio, video, and animations that last
three or more seconds at their default playback rate and that are not recognized as style.
[Priority 1] (Checkpoint
4.5)
- Note: This checkpoint applies to
content that is rendered automatically or on request from the user. Enable
control of each independent source recognized as distinct. Respect
synchronization cues per
checkpoint 2.5. Refer also to checkpoint 3.2.
-
Techniques:
-
- Allow the user to advance or rewind the presentation in increments. This is
particularly valuable to users with physical disabilities who may not have fine
control over advance and rewind functionalities. Allow users to configure the
size of the increments.
- 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.
- The user agent should display time codes or represent otherwise position in
content to orient the user.
- 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.
- Apply techniques for changing audio speed without introducing
distortion.
- Note that Home Page Reader [HPR] lets users insert bookmarks in
presentations.
-
- 4.6 For
graphical viewports, allow the user to position text
transcripts,
collated text transcripts, and
captions in the viewport. Allow the user to choose from among the
same range of positions available to the author (e.g., the range of positions
allowed by the markup or style language).
[Priority 1] (Checkpoint
4.6)
-
Techniques:
-
- Some users 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 screen magnifiers or who have other visual disabilities) require
pieces of content to be in a particular relation to one another, even if this
means that some content will obscure other content.
- User agents should implement the positioning features of the employed
markup or style sheet language. Even when a markup language does not explicitly
allow positioning, 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).
- 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.
- 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).
- Do not require users to edit the source code of the presentation to achieve
the desired effect.
-
-
4.7 Allow the user to slow the presentation rate of audio, video and
animations not covered by
checkpoint 4.4. The same speed percentage requirements of checkpoint 4.4 apply. [Priority 2] (Checkpoint
4.7)
- Note: User agents automatically satisfy
this checkpoint if they satisfy
checkpoint 4.4 for every audio, video, and animation.
-
Techniques:
- See the techniques for
checkpoint 4.4.
-
-
4.8 Allow the user to stop, pause, resume, fast advance, and fast
reverse audio, video, and animations not covered by checkpoint 4.5. [Priority 2] (Checkpoint
4.8)
- Note: User agents automatically satisfy
this checkpoint if they satisfy checkpoint 4.5 for every audio, video, and animation.
-
Techniques:
- See the techniques for
checkpoint 4.5.
-
Checkpoints for audio volume control (content accessibility):
-
4.9 Allow the user to configure and
control the global audio volume. The user must be able to choose
zero volume (i.e., silent). [Priority 1] (Checkpoint
4.9)
- Note: User agents should allow global
control of volume through available system-level controls.
-
Techniques:
-
- Use audio control mechanisms provided by the operating system. Control of
volume mix is particularly important, and the user agent should provide easy
access to those mechanisms provided by the operating system.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
- Allow the user to configure a volume level at the operating system
level.
- 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].
-
-
4.10 Allow the user to control
independently the volumes of distinct audio sources synchronized to play
simultaneously. [Priority 1] (Checkpoint
4.10)
- Note: Refer also to checkpoint 4.12.
-
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.
-
Checkpoints for synthesized speech (content accessibility):
Refer also to techniques for synthesized
speech.
-
4.11 Allow the user to configure and
control synthesized speech playback rate according to the full range
offered by the speech synthesizer.
[Priority 1] (Checkpoint
4.11)
- Note: The range of playback rates
offered by the speech synthesizer may depend on the natural language.
-
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 playback rate in convenient increments (e.g., in large steps, then
in small steps for finer control).
- User agents may allow different playback 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 system.
- Implement the CSS 2
'speech-rate' property ([CSS2], section 19.8).
-
-
4.12 Allow the user to control
synthesized speech volume independent of other sources of audio. [Priority 1] (Checkpoint
4.12)
- Note: Refer also to checkpoint 4.10.
-
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 system.
- Implement the CSS 2
'volume' property ([CSS2], section 19.2).
-
-
4.13 Allow the user to configure
synthesized voice gender, pitch, pitch range, stress, richness, speech
dictionary, and handling of spelling, punctuation, and number processing
according to the full range of values offered by the speech synthesizer. [Priority 2] (Checkpoint
4.13)
- Note: Ranges of values for these
characteristics may vary among speech synthesizers. For information about these
synthesized speech characteristics, please refer to descriptions in section
19.8 of Cascading Style Sheets Level 2 [CSS2].
-
Techniques:
-
- Use synthesized speech mechanisms provided by the operating system.
- Implement the
voice characteristic properties of CSS 2: 'voice-family', 'pitch',
'pitch-range', 'stress', 'richness', ([CSS2], sections 19.8 and 19.9).
- One example of a speech API is Microsoft's Speech Application
Programming Interface
[SAPI].
-
Checkpoints for user interface accessibility:
- 4.14
For user agents that support
style sheets, allow the user to select from (and apply) available
author and
user style sheets or to ignore them.
[Priority 1] (Checkpoint
4.14)
- Note: By definition, the user agent's default style sheet is always
present, but may be overridden by author or user styles.
-
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).
- 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].
-
- 4.15 Allow the user to configure how the
selection is
highlighted (e.g., foreground and background color, voice pitch,
etc.). For graphical viewports, offer at least three rendering options,
including colors and fonts. Allow the user to select from among the range of
system colors and fonts. [Priority 1] (
Checkpoint 4.15)
- Note: For information for control of speech output and
using those parameters for highlighting, see checkpoint 4.13.
-
Techniques:
-
- As a sample implementation, note that Netscape Navigator
[NAVIGATOR] for X Windows uses resources to control the selection
colors (
*selectForeground
and
*selectBackground
).
- Implement the CSS 2
"HighLightText and "Highlight" predefined color values ([CSS2], section
18.2).
- Inherit selection
information from user's settings for the operating system.
- A highlighted selection may span text with different background colors,
text foreground colors, font families, etc.
-
-
4.16 Allow the user to configure
how the content
focus is
highlighted (e.g., foreground and background color, voice pitch,
etc.). For graphical viewports, offer at least three rendering options,
including colors and fonts, and allow the user to select from among the range
of system colors and fonts. The default focus highlight mechanism must be
different from the default selection highlight mechanism. [Priority 1] (Checkpoint
4.16)
- Note: For information for control of speech output and
using those parameters for highlighting, see checkpoint 4.13.
-
Techniques:
-
- Implement the CSS 2
':focus' pseudo-class and dynamic outlines
and focus of CSS 2 ([CSS2], sections 5.11.3 and 18.4.1,
respectively).
For 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 }
- Inherit
focus information from user's settings
for the operating system.
- Test the user agent to ensure that individuals who have low vision and use
screen magnification software are able to follow highlighted item(s).
- A highlighted focus may span text with different background colors, text
foreground colors, font families, etc.
-
-
4.17 Allow the user to configure
whether the current
focus moves automatically to a
viewport that opens without an explicit request from the user. [Priority 2] (Checkpoint
4.17)
-
Techniques:
-
- If the focus automatically changes to a new viewport, this may disorient
users with cognitive disabilities or who are blind and it may be difficult to
navigate back to the previous point of regard.
- Allow the user to configure how 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 5.5) 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).
- 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"}
-
-
4.18 Ensure that when a viewport's
selection or content
focus changes, it is in the viewport
after the change. [Priority 2] (Checkpoint
4.18)
- 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.
-
Techniques:
-
- There are times when the content focus changes (e.g., link navigation) and
the viewport must be moved 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 explicitly, 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
and time becomes a scarce resource and the flowing of content through the
display has to be managed more carefully, which means that in accessing content
that was edited at the source for use with a graphical user interface, it
generally has to be managed actively.
- 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.
-
- 4.19 Allow the user to configure the user agent to only open viewports
on explicit
user request. In this configuration, instead of opening a viewport
automatically, alert the user and allow the user to open it manually. Allow the
user to close viewports. [Priority 2] (Checkpoint
4.19)
- 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. Refer also to checkpoint 4.17 (for control over changes of focus when a
viewport opens) and checkpoint
5.5.
-
Techniques:
-
- 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 cognitive disabilities (who may be disoriented).
- 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.
-
- 4.20 For graphical user interfaces,
allow the user to configure the user agent so that the viewport with the
current focus remains "on top" of all
other viewports. In this configuration, when a viewport opens without explicit
user request, alert the user.
[Priority 2] (Checkpoint
4.20)
-
Techniques:
-
- The alert is important to ensure that the user realizes a new viewport has
opened, since it may be hidden by the viewport configured to remain on
top.
-
Checkpoints for communication with other software:
- 5.1 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: (1) the Core module for HTML; (2) the Core and XML
modules for XML. [Priority 1] (Checkpoint
5.1)
- Note: Please refer to the "Document
Object Model (DOM) Level 2 Core Specification" [DOM2CORE]
for information about HTML and XML
versions covered.
-
Techniques:
-
- 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.
- See the appendix on loading assistive technologies
for DOM access.
- 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].
-
- 5.2 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: (1) the Core
module for HTML; (2) the Core and XML modules for XML.
[Priority 1] (Checkpoint
5.2)
- 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.
-
Techniques:
- 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. Consider an ordered
list. The Internet Explorer 5.5 [IE-WIN] document object model for
HTML tells you that list elements are part of an ordered list but does not tell
you each list element's number. The assistive technology can add the list
element number to each list entry in its attribute list, for audio rendering.
Furthermore, the assistive technology component that added the numeric
information can mark that section as having been traversed and updated to
prevent having to recompute and store the numeric information on the next pass
through by the user.
Refer also to techniques for
checkpoint 5.1.
-
- 5.3 For markup languages other than
HTML and XML, provide programmatic access
to content using standard
APIs (e.g., platform-independent APIs and
standard APIs for the operating system). [Priority 1] (Checkpoint
5.3)
- Note: This checkpoint addresses content
not covered by checkpoints
checkpoint 5.1 and
checkpoint 5.2.
-
Techniques:
-
-
- 5.4 Provide programmatic read and write
access to user
agent user interface controls using standard
APIs (e.g., platform-independent APIs
such as the W3C DOM; standard APIs defined for a specific
operating system; and conventions for programming languages, plug-ins, virtual
machine environments, etc.) [Priority 1]
(Checkpoint
5.4)
- Note: For example, provide access to
information about the user agent's current input configuration so that assistive
technologies can trigger functionalities through keyboard events,
mouse events, etc.
-
Techniques:
-
- Use standard operating system and programming language
APIs that support accessibility by
providing a bridge between the standard user interface supported by the
operating system and alternative user interfaces developed by assistive
technologies. User agents that implement these
APIs are generally more compatible with assistive technologies and
provide accessibility at no extra cost. Some public APIs that promote
accessibility 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.
- Use standard user
interface controls. Third-party assistive technology developers are
more likely able to access standard controls than custom
controls. If you must 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
standard controls.
- Make use of operating system level features. See the appendix of accessibility features for some common
operating systems.
- Provide information about the selection
and focus.
- Inherit operating system settings related to accessibility (e.g., for
fonts, colors, natural
language preferences, input configurations, etc.).
- Write output to and take input from standard system
APIs rather than directly from hardware
controls. This will enable the I/O 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.
- For information about rapid access to Internet Explorer's [IE-WIN] DOM
through COM, refer to
[BHO].
-
- 5.5 Using standard
APIs, provide programmatic alert of
changes to
content and
user interface controls (including
selection, content
focus, and user
interface focus). [Priority 1]
(Checkpoint
5.5)
- Note: For instance, when user
interaction in one frame causes automatic changes to content in another,
provide programmatic alert through standard APIs. Use the standard APIs required by guideline 5.
-
Techniques:
-
- 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].
-
- 5.6 Ensure that programmatic exchanges
proceed in a timely manner. [Priority 2]
(Checkpoint
5.6)
- Note: For example, the programmatic
exchange of information required by other checkpoints in this document must 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. The
techniques for this checkpoint explain how developers can reduce communication
delays, e.g., to ensure that assistive technologies have timely access to the
document object model and other
information needed for accessibility.
-
Techniques:
-
-
- 5.7 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. [Priority 3] (Checkpoint
5.7)
- 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.
-
Techniques:
-
-
Checkpoints for user interface accessibility:
- 5.8 Follow operating system conventions
that benefit accessibility. In particular, follow conventions for
user interface design, keyboard
configuration, product installation, and
documentation. [Priority 2] (Checkpoint
5.8)
- Note: Operating system conventions that benefit
accessibility are those described in this document and in platform-specific
accessibility guidelines. Some of these conventions (e.g., sticky keys, mouse
keys, show sounds, etc.) are discussed in the Techniques document
[UAAG10-TECHS]. Refer also to checkpoint 9.2.
-
Techniques:
-
- See techniques for
checkpoint 1.2.
- See techniques for checkpoint
5.4.
- See techniques for
checkpoint 9.2.
- Follow operating system and application environment (e.g., Java)
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.
- Ensure that any online services (e.g., automated update facilities,
download-and-install functionalities, sniff-and-fill forms, etc.) observe
relevant operating system conventions concerning device independence and
accessibility (as well as the Web Content Accessibility Guidelines 1.0 [WCAG10]).
- Evaluate the standard interface controls on the target platform against any
built-in operating system accessibility functions (refer to 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 system 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, but developers should make changes conservatively to the layout of
user interface controls,
the behavior of existing functionalities, and the default keyboard
configuration.
- 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].
-
Checkpoints for content accessibility:
-
6.1 Implement the accessibility features of all implemented specifications (markup languages,
style sheet languages, metadata languages, graphics formats, etc.). The
accessibility features of a specification are those identified as such and
those that satisfy all of the requirements of the "Web Content
Accessibility Guidelines 1.0" [WCAG10].
[Priority 1] (Checkpoint
6.1)
-
Techniques:
-
- Make obvious to users features that are known to promote 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 "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].
- Refer to the following list of accessibility features of HTML 4 [HTML4] (in
addition to those described in techniques for checkpoint 2.1):
- The
CAPTION element (section 11.2.2) for rich table captions.
- Table elements
THEAD, TBODY, and TFOOT (section 11.2.3),
COLGROUP and
COL (section 11.2.4) that group table rows and columns into meaningful
sections.
- Attributes
"scope",
"headers", and
"axis" (section 11.2.6) which are semantically significant labels that
non-graphical user agents may use to render a table in a linear fashion.
- The
"tabindex" attribute (section 17.11.1) for assigning the order of keyboard
navigation within a document.
- The
"accesskey" attribute (section 17.11.2) for assigning keyboard commands to
active components such as links and form controls.
- 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].
-
- 6.2 Use and
conform to W3C Recommendations when they are available and
appropriate for a task. [Priority 2] (Checkpoint
6.2)
- Note: For instance, for markup, conform to HTML 4 [HTML4], XHTML 1.0
[XHTML10], or XML 1.0 [XML]. For style sheets, conform to
CSS ([CSS1], [CSS2]). For mathematics, conform to
MathML
[MATHML]. For synchronized multimedia, implement
SMIL 1.0
[SMIL]. For information about programmatic access to
HTML and XML content, refer to guideline 5. User agents may
conform to other specifications in addition to those required by this
checkpoint. 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.
-
Techniques:
-
- 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.
- 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.
- W3C make available validation services to promote the proper usage and
implementation of specifications. Refer to the:
-
Checkpoints for user interface accessibility:
- 7.1 Allow the user to navigate among all
viewports (including frames). [Priority 1] (Checkpoint
7.1)
- Note: For example, when all frames of a
frameset are displayed side-by-side, allow the user to navigate among them with
the keyboard. Or, when frames are accessed or viewed one at a time (e.g., by a
text browser or speech synthesizer), provide a list of links to other frames.
Navigation among all viewports implies at least allowing the user to cycle
through all viewports. Navigating into a viewport makes it the current
viewport.
-
Techniques:
-
- See the frame techniques. Some operating
systems provide a means to navigate 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. However, user agents may
also provide a mechanism to shift the user
interface focus among user agent windows, independent of the
standard operating system mechanism.
-
-
7.2 Associate a point of
regard with each state in a viewport's browsing history and when the
user returns to a state in the history, restore the associated point of regard.
[Priority 1] (Checkpoint
7.2)
- Note: For example, when the user
navigates from one viewport to another (per checkpoint 7.1) and back, restore the point of
regard.
-
Techniques:
-
- When the user returns to a page after following a link, restore content
focus to that link.
- 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.
- Refer to the HTTP/1.1 specification for information about history
mechanisms ([RFC2616], section 13.13).
-
- 7.3 Allow the user to navigate all
active elements. If the author has not
specified a navigation order, allow at least forward sequential navigation of
elements, in document order. [Priority 1]
(Checkpoint
7.3)
- Note: Navigation may include non-active
elements in addition to active elements. This checkpoint is an important
special case of checkpoint
7.6.
-
Techniques:
-
- Allow the user to navigate sequentially all active elements 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. Refer also to checkpoint 9.4.
- 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, refer to techniques for checkpoint 8.9.
- 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.).
- 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.
- 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).
- Give the users the option of navigating to and activating a link,
or just moving the content
focus to the link. First-time users of a page may want access to
link text before deciding whether to follow the link (activate). More
experienced users of a page might prefer to follow the link directly, without
the intervening content focus step.
- 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.
- 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 control text, associated labels, or form control
names).
- Document available direct navigation mechanisms.
-
- 7.4 Allow the user to choose to navigate
only active
elements. If the author has not specified a navigation order, allow
at least forward and reverse sequential navigation of active elements, in
document order. [Priority 2] (Checkpoint
7.4)
-
Techniques:
-
-
- 7.5 Allow the user to search for a string of
characters from the
document character set in text content
that has been
rendered. The search must encompass all text within the viewport,
both inside and outside the point of
regard. Allow the user to start a search forward in document order
from any selected or focused location in content. When there is a match, allow
the user to search for the next instance of the text from the location of the
match. When there is a match, move the point of regard so that the matched text is in
the viewport. Alert the user when there is no match. Provide a case-insensitive
search option for text in scripts
(i.e., writing systems) where case is significant.
[Priority 2] (Checkpoint
7.5)
- Note: The default search starting point should be the
beginning of content. Use operating system conventions for indicating the
result of a search (e.g., selection
or content
focus).
-
Techniques:
-
- The search string input method should follow system conventions (e.g., for
international character input).
- Facilitate searches, both backward and forward, from the beginning and end
of the document as well as the point of regard.
- If the number of matches is known, provide this information to orient the
user.
- Allow users to search a document
source view.
- When the point of regard depends on time (e.g., for audio viewports), the
user must 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 information about when case is significant in a
script, please refer to Section 4.1 of Unicode
[UNICODE].
- For forms, allow users to find controls
that must be changed by the user before submitting the form. Allow users to
search the element content of controls (where applicable) and any label
text.
- Allow the user to search among just text
equivalents of other content.
- 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 find all media elements active at a particular time in the
presentation.
- Allow users to view a list of all media elements or links of the
presentations sorted by start or end time or alphabetically.
- For frames, allow users to search for content in all frames, without having
to be in a particular frame.
- 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.
-
- 7.6 Allow the user to navigate efficiently
to and among important structural elements identified by the author. Allow
forward and backward sequential navigation to important structural elements.
[Priority 2] (Checkpoint
7.6)
- Note: This specification intentionally
does not identify the set of "important elements" that must be navigable; refer
to the Techniques document [UAAG10-TECHS] for
information about identifying important elements. Structured navigation of
headings, tables, forms, lists, etc., is most effective in conjunction with a
configurable view (refer to configuration requirements of checkpoint 8.4 and checkpoint 7.7). User
agents should follow operating system conventions for indicating navigation
progress (e.g., selection
or content
focus).
-
Techniques:
-
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.
Instead, user agents are expected to construct the navigation view from
author-supplied markup. For those languages with known 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.
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 promote orientation at the same time.
- 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.
- 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.
- 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 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.
- Allow depth-first as well as breadth-first 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.).
Refer also to checkpoint
1.5.
- 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.
- From a given element, allow navigation to the next or previous sibling, up
to the parent, and to the end of an element.
- Allow users to navigate synchronized multimedia presentations. Refer also to checkpoint
4.5.
- 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].
- 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.
- The following is a summary of ideas provided by the National Information
Standards Organization [NISO]:
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.
-
- 7.7
Allow the user to configure and
control the set of important elements required by checkpoint 7.6 and checkpoint 8.4. Allow the
user to include and exclude element types in the set of elements. [Priority 3] (Checkpoint
7.7)
- Note: For example, allow the user to navigate only
paragraphs, or only headings and paragraphs, etc. Refer also to checkpoint 5.4.
-
Techniques:
-
- Allow the user to navigate by abstractions (e.g., in HTML, all heading
elements H1-H6 ).
- Allow the user to navigate HTML elements that share the
same "class" attribute.
- Allow the user to navigate according to similar styles (which may be an
approximation for similar element types).
- 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.
-
Checkpoints for content accessibility:
- 8.1 Make available to the user the
author-specified purpose of each table and the author-specified relationships
among the table cells and headers.
[Priority 1] (Checkpoint
8.1)
- Note: 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. Refer also to checkpoint
5.3. This checkpoint is an important special case of checkpoint 2.1.
-
Techniques:
-
- 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.
- Provide information about table headers, how headers relate to cells, table
summary information, cell position information, table dimensions, etc.
- 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, refer to the
section on table 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".
- 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).
-
- 8.2 Render recently visited links in a
distinct style and allow the user to configure this style. For graphical
viewports, offer at least three rendering options, including colors and fonts.
Allow the user to select from among the range of system colors and fonts. [Priority 2] (Checkpoint
8.2)
- Note: Do not use color as the only
distinguishing factor between visited and unvisited links as some users may not
perceive colors and some devices may not render them. This checkpoint is an
important special case of checkpoint
8.5.
-
Techniques:
-
-
- 8.3 Render in a distinct style those links
that have been marked up to indicate that following them will involve a fee and
allow the user to configure this style. For graphical viewports, offer at least
three rendering options, including colors and fonts. Allow the user to select
from among the range of system colors and fonts.
[Priority 2] (Checkpoint
8.3)
- Note: This checkpoint is an important
special case of checkpoint
8.5.
-
Techniques:
-
- The W3C specification "Common Markup for micropayment per-fee-links"
[MICROPAYMENT] describes how authors may mark up micropayment
information in an interoperable manner.
- Use standard, 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).
- See the section on link techniques.
-
- 8.4
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.). For discussion about what
constitutes the set of important structural elements, please refer to checkpoint 7.6. [Priority 2] (Checkpoint
8.4)
- Note: This checkpoint is meant to allow
the user to simplify the view of content by hiding some content selectively.
For example, for each frame in a frameset, provide a table of contents composed
of headings (e.g., the H1 - H6 elements in HTML) where each entry in the table
of contents links to the heading in the document. This checkpoint does not
require that the outline view be navigable, but this is recommended; refer to
checkpoint 7.6. For those
elements that do not have associated text titles or labels, the user agent
should generate a brief text label (e.g., from content, the element type,
etc.). Refer also to
checkpoint 7.7.
-
Techniques:
-
- 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.
- See structured navigation techniques for checkpoint 7.6.
- 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.
-
- 8.5 To help the user decide whether to
traverse a link, make available the following information about it: link
content, link title, whether the link is internal to the local resource,
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.
[Priority 3] (Checkpoint
8.5)
-
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.
- 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.
- Links may be simple (e.g., HTML links) or more complex, such as those
defined by the XML Linking Language (XLink) [XLINK].
- Refer to RFC 2616 [RFC2616], section 14.13.
- 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).
- See the section on link techniques.
-
Checkpoints for user interface accessibility:
-
8.6 Implement
selection, content
focus, and user
interface focus mechanisms. Implement
them according to system conventions (per checkpoint 5.8).
[Priority 1] (Checkpoint
8.6)
- Note: This checkpoint refers to the logical
selection and focus; rendering requirements are addressed by checkpoint 8.7,
checkpoint 4.16,
and checkpoint
4.15. Refer also to checkpoint
7.1.
-
Techniques:
-
-
- 8.7 Provide a mechanism
for
highlighting the current viewport,
selection, and content
focus. [Priority 1] (
Checkpoint 8.7)
- Note: This includes highlighting and
identifying frames. This checkpoint is an important special case of checkpoint 1.1. Refer
also to checkpoints checkpoint 4.15, checkpoint 5.8, and checkpoint 8.5.
-
Techniques:
-
- If colors are used to highlight the current viewport, selection, or content
focus, allow the user to configure these colors. Do not rely on color
alone.
- Provide a setting that causes a window that is the current viewport to pop
to the foreground.
- Provide a setting that causes a window that is the current viewport 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 current
window so that users have to scroll horizontally or vertically as little as
possible.
- If the current viewport 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 current viewport.
- For speech or braille output, use the frame or window title to identify the
current viewport. Announce changes in the current viewport.
- Use operating system 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.
- See the section on frame techniques.
-
- 8.8 Provide a mechanism for highlighting and identifying
active elements.
[Priority 2] (Checkpoint
8.8)
- Note: On most systems, the focus is used to identify and highlight active
elements.
-
Techniques:
-
-
- 8.9 Allow configuration so the user is
prompted to confirm any form submission not
caused by explicit
user request to activate a form submit control. [Priority 2] (Checkpoint
8.9)
- 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 event occurs. The user agent may satisfy this
checkpoint by prompting
the user to confirm all form submissions.
-
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., triggered by 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).
- 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.
- Generate an explicit form submit button when the author has not provided
one.
-
- 8.10 Indicate the relative position of
the viewport in 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.). [Priority 3] (Checkpoint
8.10)
- 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. For two-dimensional renderings,
relative position includes both vertical and horizontal positions.
-
Techniques:
-
- Provide a scrollbar for the viewport. Some specifications address scrolling
requirements or suggestions explicitly, 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 standard 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).
-
Checkpoints for user interface accessibility:
-
9.1 Provide information to the user about current user preferences
for input
configurations (e.g., keyboard or voice bindings). [Priority 1] (Checkpoint
9.1)
-
Techniques:
-
-
-
9.2 Ensure that default input configurations do not interfere with
operating system accessibility conventions.
[Priority 1] (Checkpoint
9.2)
- Note: In particular, default
configurations should not interfere with operating conventions for keyboard
accessibility. Information about operating system accessibility conventions is
available in the Techniques document [UAAG10-TECHS]. Refer also to checkpoint
5.8.
-
Techniques:
-
- The default configuration should not include
"Alt-F4",
"Control-Alt-Delete", or other combinations
that have reserved meanings on a given operating system.
- Clearly document any default configurations that depart from system
conventions.
- Some reserved keyboard bindings are listed in the appendix on accessibility features of some operating
systems.
-
-
9.3 Provide information to the user about current author-specified
input
configurations (e.g., keyboard bindings specified in HTML documents
with the "accesskey" attribute).
[Priority 2] (Checkpoint
9.3)
-
Techniques:
-
-
- 9.4 Allow the user to change the default
input
configuration as follows: Allow the user to override any binding
that is part of the user agent default input configuration (checkpoint 9.8). The user
agent is not required to allow the user to override standard bindings for the
operating system (e.g., for access to help). For any binding in the default
keyboard configuration, allow the user to override it with a binding of a
single key alone or with modifier keys.
[Priority 2] (Checkpoint
9.4)
- Note: This checkpoint applies to all supported input methods: keyboard, voice,
pointing device, etc. The override requirement only applies to bindings for the
same input method (i.e., the user must be able to override a keyboard binding
with another keyboard binding). Refer also to checkpoint 9.5, checkpoint 9.9, checkpoint 9.8, and checkpoint 10.3.
-
Techniques:
-
- See input configuration
techniques.
- Allow users to restore easily the default input configuration.
- Test the default keyboard configuration for usability. Ask users with
different disabilities and combinations of disabilities to test
configurations.
- When using a physical keyboard, some users require single-key access (refer
to checkpoint 9.5), others
require that keys activated in combination be physically close together, while
others require that they be spaced physically far apart.
- Allow users to select 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 create macros and bind them to key strokes or other input
methods.
- 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 active 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).
- 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).
-
- 9.5 Allow the user to assign a
single-key binding to at least a majority of the functionalities available in
the default keyboard configuration (refer to checkpoint 9.8). [Priority 2] (Checkpoint
9.5)
- Note: In some modes of interaction
(e.g., when the user is entering text), the number of available single keys
will be significantly reduced. The number of available single keys will also be
determined by the keyboard device capabilities. This checkpoint does not
require single-key bindings for character input, only for the activation of
user agent functionalities. This checkpoint is an important special case of checkpoint 9.4. Refer also to
checkpoint 1.3, checkpoint 9.9, checkpoint 9.8, and checkpoint 10.3.
-
Techniques:
-
- See input configuration
techniques.
- Opera
[OPERA] includes a mode in which users can access important user
agent functionalities with single strokes from the numeric keypad.
- Mouse Keys (available on some operating systems)
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.
-
-
9.6 Follow operating system conventions to indicate the input
configuration. [Priority 2] (Checkpoint
9.6)
- Note: For example, on some operating systems, developers
may specify which command sequence will activate a functionality so that the
standard user interface components display that binding. For example, if a
functionality is available from a menu, the letter of the activating key will
be underlined in the menu. This checkpoint is an important special case of checkpoint 5.8.
-
Techniques:
-
- See input configuration
techniques.
- Use system 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 trigger 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 currently active 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 active 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.
-
- 9.7 For the configuration requirements of
this document, allow the user to save user preferences in at least one user profile. Allow users to select from among
available profiles or no profile (i.e., the user agent default settings). [Priority 2] (Checkpoint
9.7)
- 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
alerts.
-
Techniques:
-
- Follow applicable operating system 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.
-
- 9.8
Ensure that the default input
configuration includes bindings for the following functionalities
required by other checkpoints in this document: move focus to next active
element; move focus to previous active element; activate focused link; search
for text; search again for same text; next history state (forward); previous
history state (back); increase size of rendered text; decrease size of rendered
text; increase global volume; decrease global volume; (each of) stop, pause,
resume, fast advance, and fast reverse selected audio, video, and animation. If
the user agent supports
the following functionalities, the default input configuration must also
include bindings for them: enter URI for new resource; add to favorites (i.e.,
bookmarked resources); view favorites; stop loading resource; reload resource;
refresh rendering; forward one viewport; back one viewport; next line; previous
line. [Priority 2] (Checkpoint
9.8)
-
Techniques:
-
- Provide different input configuration profiles
(e.g., one keyboard profile with key combinations close together and another
with key combinations far apart).
- 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.).
- 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.
- Offer a mode that makes the input configuration compatible with other
versions of the software (or with other software).
- Refer also to
checkpoint 9.6.
-
- 9.9 For graphical user interfaces,
allow the user to configure
the position of controls on tool bars of the user agent user interface, to select or remove
controls for the user interface from a predefined set, and to restore the
default user interface. [Priority 3] (Checkpoint
9.9)
- Note: This checkpoint is an important special case of checkpoint 9.4.
-
Techniques:
-
- Allow multiple icon sizes (big, small, other sizes).
- Allow the user to choose icons and/or text.
- Allow the user to change the grouping of icons.
- 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 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 for accessible documentation:
- 10.1 Ensure that at least one version of
the product
documentation conforms to at least Level Double-A of the Web Content
Accessibility Guidelines 1.0 [WCAG10].
[Priority 1] (Checkpoint
10.1)
-
Techniques:
-
- 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].
- Distribute accessible documentation over the Web, on CD-ROM, or by
telephone. Alternative hardcopy formats may also benefit some users.
- Documentation includes information bundled with a product when it is
released as well as information made available subsequently (e.g., bug fixes,
etc.).
- Web-based support and/or documentation that is produced or maintained by
the manufacturer of a user agent or by a sub-contractor of the user agent's
developer must conform to the Web Content Accessibility Guidelines 1.0 [WCAG10]. In
particular:
- 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;
- Refer also to
checkpoint 10.3.
- 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 system conventions for input configurations
related to run-time help.
- 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.
- 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.
- Ensure that product identification codes are accessible to users so they
may install their software. Codes printed on product cases may not be
accessible to people with visual disabilities.
-
-
10.2
Document all user agent features that promote accessibility. [Priority 1] (Checkpoint
10.2)
- Note: For example, review the
documentation or help system to ensure that it includes information about the
functions and capabilities of the user agent that are required by WAI Guidelines.
-
Techniques:
-
- Refer also to techniques for checkpoint 10.4.
- 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.
- In developer documentation, document the APIs that are required by this
document. Please refer to the requirements of checkpoint 1.2, checkpoint 5.1,
[+T+1content-access-api], and [+T+1ui-access-api].
-
-
10.3
Document the default input configuration (e.g., default keyboard
bindings). [Priority 1] (Checkpoint
10.3)
-
Techniques:
-
The following table shows how one might document keyboard bindings. It shows
the default keyboard configuration for versions of Netscape Navigator
[NAVIGATOR] running on the Macintosh, Unix, and Windows operating
systems. If a function exists in the browser but does not have a binding, its
corresponding cell is marked with an asterisk. If the function does not exist,
it is left blank. Note: This table lists some, but not all,
functionalities and keyboard bindings of Navigator. It is meant to illustrate,
not serve as definitive documentation for Netscape Navigator.
Some entries contain links to special notes. The number in parentheses
following the link is the number of the relevant note.
Note: To make this table accessible, a linear version of Navigator Keyboard
Bindings is available.
Navigator Keyboard Bindings
Function |
Macintosh (v 4.61) |
Unix (v 4.51) |
Windows (v 4.7) |
Move within a document |
Scroll to next page |
Page Down |
Page Down |
Page Down |
Scroll to previous page |
Page Up |
Page Up |
Page Up |
Scroll to top |
* |
* |
Control-Home |
Scroll to bottom |
* |
* |
Control-End |
Move between documents |
Open a new document |
Command+L |
Alt+O |
Control+O |
Stop loading a document |
Command+. |
Esc |
Esc |
Refresh a document |
Command+R |
Alt+R |
Control+R |
Load previous document |
Command+[
or
Command+Left Arrow |
Alt+Left Arrow |
Alt+Left Arrow |
Load next document |
Command+]
or
Command+Right Arrow |
Alt+Right Arrow |
Alt+Right Arrow |
Navigate elements within a document |
Move focus to next frame |
* |
* |
* |
Move focus to previous frame |
* |
* |
* |
Move focus to next active element
(1) |
Tab |
Tab |
Tab |
Move focus to previous active element
(1) |
Shift+Tab |
Shift+Tab |
Shift+Tab |
Find word in page |
Command+F |
Alt+F |
Control+F |
Act on HTML elements |
Select a link |
* |
* |
Enter |
Toggle a check box |
* |
* |
Shift or Enter |
Activate radio button |
* |
* |
Shift |
Move focus to next item in an option box |
* |
* |
Down Arrow or Right Arrow |
Move focus to previous item in an option box |
* |
* |
Up Arrow or Left Arrow |
Select item in an option box |
* |
* |
Enter |
Press a button (2) |
Return, Space |
Enter, Space |
Enter, Space |
Navigate menus |
Activate menu |
* |
* |
Alt+ the underlined letter in the menu title |
Deactivate menu |
* |
Esc |
Esc |
Move focus to next menu item |
* |
* (3) |
Down Arrow |
Move focus to previous menu item |
* |
* (3) |
Up Arrow |
Select menu item |
* |
underlined letter in the menu item |
Enter |
Move focus to submenu |
* |
* (3) |
Right Arrow |
Move focus to main menu |
* |
* (3) |
Left Arrow |
Navigate bookmarks |
View bookmarks menu |
* (4) |
* |
Alt+C+B |
Move focus to next item in bookmarks menu |
Down Arrow (4) |
* |
Down Arrow |
Move focus to previous item in bookmarks menu |
Up Arrow (4) |
* |
Up Arrow |
Select item in bookmarks menu |
Return (4) |
* |
Enter |
Add bookmark |
Command+D |
Alt+K |
Control+D |
Edit bookmarks |
Command+B |
Alt+B |
Control+B |
Delete current bookmark (5) |
Delete |
Alt+D |
Delete |
Navigate history list |
View history list |
Command+H |
Alt+H |
Control+H |
Move focus to next item in history list |
* |
* |
Down Arrow |
Move focus to previous item in history list |
* |
* |
Up Arrow |
Move focus to first item in history list |
* |
* |
Left Arrow |
Select item in history list |
* |
* |
Enter (6) |
Close history list |
Command+W |
Alt+W |
Control+W |
Define view |
Increase font size (7) |
Shift+Command+] |
Alt+] |
Control+] |
Decrease font size (7) |
Shift+Command+[ |
Alt+[ |
Control+[ |
Change font color |
* |
* |
* |
Change background color |
* |
* |
* |
Turn off author-defined style sheets |
* |
* |
* |
Turn on user-defined style sheets
(8) |
? |
? |
? |
Apply next user-defined style sheet |
? |
? |
? |
Apply previous user-defined style sheet |
? |
? |
? |
Other functionalities |
Access to documentation |
* |
* |
* |
-
Notes.
- In Windows,
active elements of the user interface include links,
text entry boxes, buttons, checkboxes, radio buttons, etc. In Unix
and Macintosh, Tab cycles through text entry boxes only.
- In Windows, this
works for any button, since any button can gain the user interface focus using keyboard commands.
In Unix and Macintosh, this only applies to the "Submit" button following a
text entry.
- the menus
cannot be opened with binding keys. However, once a menu is opened it stays
opened until it is explicitly closed, which means that the menus can still be
used with shortcut keys to some extent. Sometimes left and right arrows move
between menus and up and down arrows move within menus, but this does not seem
to work consistently, even within a single session.
- In Macintosh,
you cannot explicitly view the bookmarks menu. However, if you choose "Edit
Bookmarks", which does have a keyboard binding, you can then navigate through
the bookmarks and open bookmarked documents in the current window.
- To delete
a bookmark you must first choose "Edit Bookmarks" and then move the focus to the bookmark you want to delete.
- In Windows,
when you open a link from the history menu using Enter, the document
opens in a new window.
- All three systems have
menu items (and corresponding shortcut keys) meant to allow the user to change
the font size. However, the menu items are consistently inactive in both
Macintosh and Unix. The user seems to be able to actually change the font sizes
only in Windows.
- It is
important to allow users to set their own Cascading Style Sheets. Although
Navigator does currently allow the user to override the author's choice of
foreground color, background color, font, and font size, it does not allow some
of the advanced capabilities that make CSS so powerful. For
example, a blind user may want to save a series of style sheets which show only
headings, only links, etc., and then view the same page using some or all of
these style sheets in order to orient himself to the organization of the page
before reading the page.
-
-
10.4 In a dedicated section of the
documentation, describe all features of the user agent that promote
accessibility. [Priority 2] (Checkpoint
10.4)
- Note: This is a more specific
requirement than
checkpoint 10.2.
-
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.
-
- 10.5 In each software release,
document all changes that affect
accessibility. [Priority 2] (Checkpoint
10.5)
- Note: Features that affect accessibility are listed in
this document and in platform-specific accessibility guidelines.
-
Techniques:
-
- At a minimum provide a text description of changes (e.g., in a README
file).
- In particular, document changes to the user interface.
-
This section presents general accessibility techniques that may apply to
more than one checkpoint.
User agents must 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?)
- Providing access to equivalents,
- 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) must also make those relationships apparent,
otherwise users may not understand the purpose of the table and the
relationships among its cells (refer to the section on table techniques). User agents must 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 is
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 must 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
(e.g., with the mouse) and opens an attribute menu that shows which attributes
are available for the element and which are set. The user may read or write
values to attributes (since Amaya is an editor). 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 provide
equivalents to content so that users may understand the function of
a page or part of a page even though they may not be able to make use of a
particular content type. For example, authors must provide text equivalents for
non-text
content (e.g., images, video, audio-only presentations, etc.) because text may be rendered as speech or braille and
may be used by users with visual or hearing or both disabilities. User agents
must ensure that these equivalents are available to users, either through the
user interface or through an API.
How authors specify
equivalents depends on the markup language used. For information
about equivalents for SMIL [SMIL] content, refer to
"Accessibility Features of SMIL" [SMIL-ACCESS]. In
HTML 4
[HTML4], authors specify equivalents as follows:
Techniques for providing access to equivalents include the following:
- Make information available with different levels of detail. For example,
for a voice browser, offer two options for equivalent alternatives to
HTML images:
- 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 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 equivalent
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 multimedia presentations with several alternative tracks, allow users
to select 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).
- For missing
equivalents:
- The "Altifier Tool" [ALTIFIER] illustrates smart
techniques for generating text
equivalents (for images, etc.) when the author has not specified
any.
- If no captioning information is available and captioning is turned on,
render "no captioning information available" in the captioning region of the
viewport.
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. Refer also to 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 (refer to
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 must 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 must 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.
- For animations, allow users to control the rate of animation, to pause and
play animations, to step through the animation, and to play it at the specified
rate.
- Allow the user to pause a video presentation, to move, resize, and position
tracks that appear on the screen (including captions, subtitles and signed
translations) and to apply CSS stylesheets to text-based presentation.
- In the user interface:
- Allow the user to select large or small buttons and controls. Ensure that
these values are applied consistently across the user interface.
- Allow the user to regroup buttons and controls, and reorder menus.
- Use standard operating system controls for allowing configuration of font
sizes, speech rates, and other style parameters.
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 links with non-text
content such as images, make available a text equivalent as follows:
- If the author has specified a non-empty text equivalent for the image
(e.g., "alt" in HTML), use that as the link text;
- Otherwise, use the link title if available;
- Otherwise, use title information of the designated
Web resource (e.g., the TITLE element of
HTML for links to HTML documents).
- Otherwise, render part of the filename or URI of the designated
Web resource.
- Otherwise, insert a generic placeholder (e.g., [LINK]) in place of the
image.
- For an image in link content, ensure that the user has access to the link
and any long description associated with the
image.
- Ensure that all information about a link is available in a
device-independent manner. For example, 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.).
- 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.
- If the focus is used to select active elements, 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:" }').
Refer also to techniques for generated
content.
- Do not mark all local links (to anchors in the same page) as visited when
the page has been visited.
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 must 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
document source through an API (refer to checkpoint 5.3).
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 can
be considered 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). Refer also
to 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.
3.5.4
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.
3.5.5
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:
- TH cells on both the left and right of the table need to be
considered.
- For TH cells with "rowspan" set: the content of those TH cells must be
considered for each of the N-1 rows below the one containing that TH
content.
- An internal TH surrounded by TDs 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 with "colspan" set needs to be included in the list of THs 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 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 a (non-null) text equivalent is available (the "alt"
attribute), use it as the content of a generated link.
- When the author has specified a null text equivalent, do not render the
link.
- When the author has not specified a text equivalent, render (for example)
"Map area" 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 text equivalent 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 must be able to navigate from frame to frame in a device
independent manner.
- Orientation. Users need to know what frame they are in (thus, frames must
be titled), 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 the author-specified frame equivalents (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 equivalent 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 current frameset (e.g., with a thick border, by displaying
the name of the current frameset in the status bar, etc.)
- Allow the user to query the current frame 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 global list of links to frames). Note:
Recall that the user must be able to navigate frames through all supported
input devices.
- Allow navigation to frame equivalents.
- Allow the user to bookmark the current frame.
- 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 frames with
scrolling="no"
.
In this case, the user agent must 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:
<!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]:
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 is the current frame 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 forms accessible, user agents need to ensure that users may interact
with them in a device-independent manner, that users can navigate to the
various form controls, and that information about the form and its controls is
available on demand.
- 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 control (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 controls (e.g., those grouped
by LEGEND or OPTGROUP in HTML) along with their labels.
- For labels explicitly associated with form controls (e.g., "for" attribute
on LABEL in HTML), make available label information when the user navigates
among the form controls.
- As the user navigates to a form control, provide information about whether
the control must be activated before form submission.
- Allow the user to navigate away from a menu without selecting any option
(e.g., by pressing the Escape key).
- As the user navigates to a form control, provide information (e.g., through
context-sensitive help) about how the user can activate the control. Provide
information about what is required for each form control. Lynx [LYNX] conveys this
information by providing information about the currently selected form control
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 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.
Provide the following information about the controls in a form on demand
(e.g., for the control with focus):
- Indicate the number of controls in the form.
- Indicate the number of controls that have not yet been completed.
- Provide a list of controls that must be activated before form
submission.
- Provide information about the order of form controls (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 control has focus (e.g., "control 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 controls know whether they have completed the form.
- Allow the user to query a form control 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 controls 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 control. 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 controls. 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.
Some users do not want forms to be submitted without their consent. The
following techniques address user control of form submissions:
- Allow the user to turn off scripts, as 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 controls.
- Offer a configuration to prevent (or allow) automatic submission of
forms.
- Allow the user to request confirmation before any form submission not
explicitly requested by the user. This should be the default
setting. Allow the user to suppress future prompts or to change the setting to
"always/never/prompt".
- Be aware that users may inadvertently pressing the Return or
Enter key and accidentally submit a form.
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)
For 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.
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 may appear 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 that appears in the document
object must be accessible. For example, if the user agent inserts a
graphical placeholder 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]).
Refer 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 must 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 must user agents make available
equivalents to dynamic content, they must allow users to turn off
scripts, to stop animations, adjust timing parameters, etc.
Certain elements of a markup language may have associated event handlers
that are triggered when certain events occur. User agents must be able to
identify those elements with event handlers statically associated (i.e.,
associated in the document source, 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
events may be triggered by (and trigger) focus/blur events. Similarly, allow
the user to use a key command, such as "enter" and "Shift-enter" to
trigger "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 triggering that event from 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 controls, which can be triggered 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)
- Allow the user to stop and start the flow of changes made by scripts.
Prompt the user for confirmation of a pending change. Note:
Some user agents allow users to turn off scripts for security reasons.
- Document the effects of known important scripts to give users an idea in
advance of what they do. Make script source available to users so that those
familiar with the scripting language may be able to understand their
effects.
When a user agent loads an applet, it should support the Java system
conventions for loading an assistive technology (refer to 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 must
make
equivalents available to the assistive technology. Applets generally
include an application frame that provides title information.
Many people benefit from direct access to important user agent
functionalities (e.g., via a single key stroke or short voice command): users
with poor physical control (who might mistakenly repeat a key stroke), users
who fatigue easily (for whom key combinations involve significant effort),
users who cannot remember key combinations, and any user who wants to operate
the user agent efficiently.
User agents that allow users to modify default input configurations must
account for configuration information from several sources: user agent
defaults, user preferences, author-specified configurations, and operating
system 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 system
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 10.3 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 current viewport 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 must be
accessible: do not rely on color alone to convey information, use standard
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 triggered (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 possible options user agents may make available to the user to resolve
conflicts include:
- 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
trigger mechanism may conflict with system conventions. For example, Internet
Explorer
[IE-WIN] in Windows uses the Alt key as the trigger key
for author-specified bindings. If the author has specified a configuration with
the characters "h" or "f", this will interfere with the system 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 trigger
key (either globally or on a per-document basis when conflicts are
detected).
Users may want to use a keyboard or voice binding to shift focus without
actually triggering the associated functionality (refer to parallel behavior
described for navigation of active elements in the section on sequential navigation techniques). First-time users may
want to access additional information before deciding whether to activate a
control. More experienced users or those familiar with a page may want to
select and activate in one step. Therefore, the user agent may provide the user
with the following options:
- On invocation of the input binding, move focus to the associated active
element, but do not activate it.
- On invocation of the input binding, move focus to the associated active
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 active
element and activate it.
The following techniques apply to user agents that render content as
synthesized speech. For information about speech recognition and accessibility,
refer to "Speak to Write" [SPEAK2WRITE]. For more
information about voice browser technology developed at W3C, refer to "Voice
Browsers: An introduction and glossary for the requirements drafts"
[VOICEBROWSER].
- 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 for which the author has
provided no text
equivalent, 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. Note: A user agent may not support all
languages.
- 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."
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; refer to checkpoint 2.2). 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 select a state of the United States by its precise
longitude and latitude, it is just as possible to allow them to select state by
name.
Several operating systems now 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
active window 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
standard input devices/methods.
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 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.
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 (refer to checkpoint 5.6). 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:
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.
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 explicitly 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-proc 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.
/* 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].
-
Active element
- An active element is an element with behaviors that may be
activated (or
"triggered") either through the user interface or through an
API (e.g., by using scripts). Some
element instances may be active at times but not at others (e.g., they may be
"deactivated" through scripts, or they may only be active for a period of time
determined by the author). Which elements are active depends on the document
language and whether the features are supported by the user agent. In
HTML 4
[HTML4] documents, for example, active elements include links, image
maps, form controls, element instances with a value for the "longdesc"
attribute, and element instances with scripts (event handlers) explicitly
associated with them (e.g., through the various "on" attributes). Most systems
use the content focus to navigate active elements and identify which is to be
activated. An active element's behavior may be triggered through any number of
mechanisms, including the mouse, keyboard, an API, etc. The effect of activation depends on
the element. For instance, when a link is activated, the user agent generally
retrieves the linked Web
resource. When a form control is activated, it may change state
(e.g., check boxes) or may take user input (e.g., a text entry field). Refer
also to the definition of event
handler.
-
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 1.5 for
requirements about alerts.
- Application
Programming Interface (API), standard input/output/device
API
- An application programming interface (API) defines how
communication may take place between applications.
As part of encouraging interoperability, this document recommends using
standard APIs where possible, although this document does
not define in all cases how those APIs are standardized (i.e., whether they are
defined by specifications such as W3C Recommendations, defined by an operating
system vendor, de facto standards, etc.). Implementing
APIs that are independent of a particular operating system (e.g., 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 standard APIs defined for a particular operating system may reduce
implementation costs for assistive technology developers who wish to
interoperate with more than one piece of software running on that operating
system.
A "device API" defines how communication may take place
with an input or output device such as a keyboard, mouse, video card, etc. A
"standard device API" is one that is considered standard for that particular
device on a given operating or windowing system.
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 "standard input/output API" is one that is
expected to be implemented by software running on a particular operating
system. Standard input/output APIs may vary from system to system. For example,
on desktop computers today, the standard input APIs are for
the mouse and keyboard. For touch screen devices or mobile devices, standard
input APIs may include stylus, buttons, voice, etc. The
graphical display and sound card are considered standard ouput devices for a
graphical desktop computer environment, and each has a standard
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.
-
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, Audio object
- An audio object is content rendered as sound through an
audio
viewport.
- Audio-only
presentation
- An audio-only presentation is a
presentation 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 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 is either a prerecorded human
voice or a synthesized voice (recorded or generated dynamically) describing the
key visual elements of a movie or 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 called "closed captions") are text
transcripts that are
synchronized with other audio 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.
- Collated text
transcript
- A collated text transcript is a text equivalent of a movie or 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). Refer also to the definitions of text transcript and auditory
description. Collated text transcripts are essential for individuals
who are deaf-blind.
-
Configure and
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 must 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 system
or hardware limitations.
Both configuration and control may apply at different "levels": across
Web resources (i.e., at the user agent
level, or inherited from the system), to the entirety of a Web resource, or to
components of a Web resource (e.g., on a per-element basis). For example, users
may 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, the user may wish to configure
the rendering of a particular element type, which may be done through style
sheets. Or, the user may wish to control the text size dynamically (zooming in
and out) for a given document, without having to reconfigure the user agent.
Or, the user may wish to control the text size dynamically for a given element,
e.g., by navigating to the element and zooming in on it.
User agents may allow users to select configurations based on various
parameters, such as hardware capabilities, natural language, etc.
Note: In this document, the noun "control" means "user
interface component" or "form component".
-
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.
-
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
- 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.
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, Document source view
- 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", as the result of opening a local resource, etc.). A
"document source view" generally renders the document source as text written in
the markup language(s) used to build it. The document source is generally a
subset of the document
object (e.g., since the document object may include
repair content).
-
Documentation
- Documentation refers to all information
provided by the vendor about a product, including all product manuals,
installation instructions, the help system, and tutorials.
-
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).
-
Equivalent (for content)
- In the context of this document, an equivalency
relationship between two pieces of content
means that one piece -- the "equivalent" -- is able to serve essentially the
same function for a person with a disability (at least insofar as is feasible,
given the nature of the disability and the state of technology) as the other
piece -- the "equivalency target" -- does
for a person without any disability. For example, the text "The Full Moon"
might convey the same information as an image of a full moon when presented to
users. If the image is part of a link and understanding the image is crucial to
guessing the link target, then the equivalent must also give users an idea of
the link target. Thus, an equivalent is provided to fulfill the same function
as the equivalency target.
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.).
Please refer to the definitions of text
content and non-text
content for more information.
- Each markup language defines its own mechanisms for
specifying 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 system, etc. Some markup languages allow
authors to specify that a script, called an event handler, be executed when
the event occurs. 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 several checkpoints in this document, the term "explicit user request"
is used to mean any user interaction
recognized with certainty to be for a specific purpose. For
instance, when the user selects "New viewport" in the user agent's user
interface, this is an explicit user request for a new viewport. On the other
hand, it is not an explicit request when the user activates a link and that
link has been marked up by the author to open a new viewport (since the user
may not know that a new viewport will open). Nor is it an explicit user request
even if the link text states "will open a new viewport". Some other examples of
explicit user requests include "yes" responses to prompts from the user agent,
configuration through the user agent's user interface, activation of known form
submit controls, and link activation (which should not be assumed to mean more
than "get this linked resource", even if the link text or title or role
indicates more). Some examples of behaviors that happen without explicit user
request include changes due to scripts. Note: Users make
mistakes. For example, a user may submit a form inadvertently by activating a
known form submit control. In this document, this type of mistake is still
considered an explicit user request.
-
Focus,
content focus,
user interface focus, current focus
- The notion of focus refers to two identifying mechanisms
of user agents:
- The "content focus" designates an
active element in a document (e.g., a link or radio button). A
viewport has at most one content focus.
- The "user interface focus" designates a control of the user interface that
will respond to user input (e.g., a radio button, text box, menu, etc.).
In this document, the term "focus" by itself encompasses both types of focus.
Where one is meant specifically in this document, it is identified.
When several viewports coexist, each may have a content and user interface
focus. At all times, only one content focus or one user
interface focus is active, called the current focus. The current focus responds
to user input and may be toggled between content focus and user interface focus
through the keyboard, pointing device, etc. Both the content and user interface
focus may be
highlighted. Refer also to the definition of point of regard.
-
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 and which viewport is the current viewport. 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 trigger 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 part of the user agent
documentation (per checkpoint 10.3]).
-
Multimedia Presentation
- For the purposes of this document, a multimedia
presentation is a
presentation that is not a visual-only presentation,
audio-only presentation, or tactile-only presentation. In a "classic"
multimedia presentation (e.g., a movie that has sound track or an animation
with accompanying audio), at least one
visual track is closely
synchronized with at least one
audio track.
-
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).
- Refer also to the definition of script.
-
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 use the focus,
selection, or other means to designate the point of regard. A user
agent should not change the point of regard unexpectedly as this may disorient
the user.
-
Presentation
- In this document, the term presentation refers to a
collection of information, consisting of one or more
Web resources, intended to be rendered
simultaneously, and identified by a single URI. In general, a presentation has
an inherent time component (i.e., it's not just a static "Web page" (refer to
the definition of "Web page" in "Web Characterization Terminology and
Definitions Sheet" [WEBCHAR]).
-
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. On
systems 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, don't ever do X but tell me when
you could have done X but didn't, don't ever do X and don't tell me, 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, voice inflection, 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
- A user agent is said to recognize a piece of information
when the user agent developer has designed it to handle that information. A
user agent recognizes those features of markup or style languages that it
implements and the behavior of the user interface controls that it provides.
User agents may not understand everything the author has encoded in content,
such as the semantics of XML elements unknown to the user agent, whether the
link text and link title accurately describe the linked resource, whether a
sentence (that has not been specially marked up) is a text equivalent for an
image, or whether a script is calculating a factorial. A user agent does not
recognize everything that a script does, even though it may implement the scripting language. However, it
will recognize some information encoded in scripts, such as code to open a
viewport or retrieve a resource from the Web. The Techniques document
[UAAG10-TECHS] lists some markup known to affect accessibility that
should be recognized by user agents.
-
Rendered content
- The rendered content is the part of
content that can be perceived by a user through a given viewport
(whether visual, auditory, or tactile).
- Note: 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 or
as the result of a user preference. "Repair text" means repair content
consisting only of text. This
document does not require user agents to include repair content in the document
object.
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 text
equivalents, 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.);
Some user preferences may change content, such as when the user has turned
off support for images and a placeholder icon appears in place of each image
that has not been loaded.
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."
- Selection, current
selection
- The selection generally identifies a range of content
(e.g., text, images, etc.) in a document. The
selection may be structured (based on the document tree) or
unstructured (e.g., text-based). Content may be selected through user
interaction, scripts, etc. The selection may be used for a variety of purposes:
for cut and paste operations, to designate a specific element in a document, to
identify what a screen reader should read, etc.
The selection may be set by the user (e.g., by a pointing device or the
keyboard) or through an application programming interface (API). A viewport has
at most one selection (though the selection may be rendered graphically as discontinuous text fragments).
When several viewports coexist, each may have a selection, but only one is
active, called the current selection.
On the screen, the selection may be
highlighted using colors, fonts, graphics, magnification, etc. The
selection may also be rendered as inflected speech, for example.
- 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 explicit conformance
requirements (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.
-
Tactile object
- A tactile object is output from a tactile viewport. Tactile objects include text (rendered as braille) and graphics
(rendered as raised-line drawings).
- Tactile-only
presentation
- A tactile-only presentation is a
presentation consisting exclusively of
one or more tactile
tracks presented concurrently or in series.
-
Tactile track
- A tactile track is a
tactile object that is intended as a whole or partial
presentation. This does not necessarily
correspond to a single physical or logical track on the storage or delivery
media.
-
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
- In this document, the term "text element" means content that, when rendered, is understandable
in each of three modes to three reference groups:
- visually-displayed text, for users who are deaf and adept in reading
visually-displayed text;
- synthesized speech, for users who are blind and adept in use of synthesized
speech;
- braille, for users who are deaf-blind and adept at reading braille.
In these definitions, a text element is said to be "understandable" when it
fulfills its communication function to representatives of the three reference
groups. Furthermore, these definitions make assumptions such as the
availability of appropriate hardware and software, that content represents a
general mix of purposes (information, education, entertainment, commerce), that
the individuals in the groups are able to understand the natural language of
the content, that the individuals in the groups are not required to have
specialized skills (e.g., a computer science degree, etc.).
A text element may contain markup for style (e.g., font size or color),
structure (e.g., heading levels), and other semantics. However, the essential
function of the text element should be retained even if style information
happens to be lost in rendering. In this document, the term "text content"
refers to content that is composed of one or more text elements. A "non-text
element" is an element that fails to be understandable when rendered
in any of three modes to their respective reference disability
audiences. Thus, text elements have essential accessibility advantages often
associated with
text while non-text elements are those
that lack one or more such advantages.
In this document, the term "non-text content" refers to content that is
composed of one or more non-text elements. Per checkpoint 1.1 of "Web Content
Accessibility Guidelines 1.0" [WCAG10], authors must provide a
text equivalent for every author-supplied non-text element. Similarly, user
agent developers must provide a text equivalent for every non-text element
offered by the user agent to the user (refer to checkpoint 1.5).
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). For
example, in principle, a text element can be generated or encoded in any
fashion as long as it has the proper output characteristics. In general, text
elements are composed of text (i.e., a
sequence of characters). Both text elements and non-text elements should be
understood as "pre-rendering" content in contrast to the "post-rendering"
content that they produce.
A "text equivalent" is a text element that, when rendered, serves
essentially the same function as some other content (i.e., an equivalency
target) does for a person without any disability. Similarly, a
"non-text equivalent" is a non-text element that, when rendered, serves
essentially the same function as the equivalency target does for a person
without any disability. Please refer also to the definition of
equivalent.
-
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 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). Refer also to
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 and mechanisms offered by the user
agent for user interaction, such as menus, buttons, keyboard access, etc.
- the "content user interface", i.e., the
active elements that are part of content, such as form controls,
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 object
- A visual object is output from a visual viewport. Visual objects include graphics,
text, and visual portions of movies and animations.
- Visual-only
presentation
- A visual-only presentation is a
presentation consisting exclusively of
one or more visual
tracks presented concurrently or in series.
-
Visual track
- A 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 or software object. A visual track
can be text-based or graphic, static or animated.
- Views,
viewports, and current viewport
- User agents may handle different types of content: markup language, sound, video, etc.
The user views rendered
content through a
viewport, which may be a window, a frame, a piece of paper, a
loudspeaker, a virtual magnifying glass, etc. A viewport may contain another
viewport (e.g., nested frames). Viewports do not include user interface
controls such as prompts, menus, alerts, etc.
The viewport that contains both the
current focus and the current selection is called the current
viewport. The current viewport is generally highlighted when several viewports coexist. A
user agent must provide mechanisms for accessing all content that can be
presented by each viewport (e.g., scrolling mechanisms, advance and rewind,
etc.).
- 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.
-
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) as defined in 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.
- [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.
- [UAAG10]
- "Techniques for User
Agent Accessibility Guidelines 1.0", J. Gunderson, I. Jacobs, eds.
The latest draft of the guidelines is available at
http://www.w3.org/WAI/UA/UAAG10-TECHS/.
- [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.
- [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.
- [MATHML]
- "Mathematical
Markup Language", P. Ion and R. Miner, eds., 7 April 1998. This W3C
Recommendation is http://www.w3.org/TR/1998/REC-MathML-19980407.
-
[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.
- [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.
- [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.
-
[UAAG10-TECHS]
- "Techniques for User
Agent Accessibility Guidelines 1.0", J. Gunderson, I. Jacobs, eds.
The latest draft of the techniques document is available at
http://www.w3.org/WAI/UA/UAAG10-TECHS/.
- [UNICODE]
- The Unicode Consortium. "The Unicode Standard, Version 3.0", Reading, MA,
Addison-Wesley Developers Press, 2000. ISBN 0-201-61633-5. Refer also to
http://www.unicode.org/unicode/standard/versions/.
-
[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.
- [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.
- [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.
- [NISO]
- 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.
-
[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.
- [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.
- [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.
- [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.
- [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), Kitch Barnicle, Harvey Bingham, Dick Brown (Microsoft), Al
Gilman, Jon Gunderson (Chair of the Working Group, University of Illinois,
Urbana-Champaign), Eric Hansen (Educational Testing Service), Ian Jacobs (Team
Contact, W3C), Marja-Riitta Koivunen, Tim Lacy (Microsoft), Charles
McCathieNevile (W3C), Mark Novak, David Poehlman, Mickey Quenzer (isSound),
Gregory Rosmaita (Visually Impaired Computer Users Group of New York City),
Madeleine Rothberg, and Rich Schwerdtfeger.
Many thanks to the following people who have contributed through review and
past participation in the Working Group: Paul Adelson, Olivier Borius, Judy
Brewer, 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, Peter Korn, Josh Krieger, Catherine Laws, Greg
Lowney, Susan Lesch, Scott Luebking, William Loughborough, Napoleon Maou, Peter
Meijer, Karen Moses, Masafumi Nakane, Charles Oppermann, Mike Paciello, David
Pawson, Michael Pederson, Helen Petrie, Michael Pieper, Jan Richards, Hans
Riesebos, Joe Roeder, Lakespur L. Roca, 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.