User Agent Accessibility Guidelines 1.0
W3C Working Draft 7 May 2000
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- Jon Gunderson, University of Illinois at
Ian Jacobs, W3C
©1999 - 2000 W3C® (MIT,
INRIA, Keio), All Rights
Reserved. W3C liability,
use and software
licensing rules apply.
The guidelines in this document explain to developers how to design user agents that are accessible to people with
disabilities. User agents include graphical
desktop browsers, multimedia players, text browsers, voice browsers, plug-ins,
and other assistive
technologies that provide access to Web
content. While these guidelines primarily address the accessibility
of general-purpose graphical user agents, the principles presented apply to
other types of user agents as well. Following these principles will help make
the Web accessible to users with disabilities and will benefit all users.
This document is part of a series of accessibility documents published by
the Web Accessibility Initiative (WAI) of the World Wide Web
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 Working Draft follows the Proposed Recommendation review of User Agent
Accessibility Guidelines 1.0, which ended 7 April 2000. Since that date, the
Working Group has endeavored to resolve the issues raised during the review.
This release of the document incorporates resolutions as of 4 May 2000 and is
intended for review by the Working Group to evaluate whether the resolutions
are accurately represented. A history of changes to
this document is available on the Web.
Note: Three checkpoints in this document (checkpoint 5.1, checkpoint 5.2, and checkpoint 5.7) refer to the W3C DOM
Level 2 [DOM2]
specification, which is a Candidate Recommendation as of 7 May 2000. The User
Agent Guidelines Working Group continues to track the progress of that
specification and expects to maintain its dependency on DOM Level 2 if that
specification advances to Proposed Recommendation before the UA Working Group
has resolved its open issues. At its 25 April 2000 teleconference, the Working
Group resolved that it may modify the checkpoints in question to depend on DOM
1 if that will accelerate the progress of this document.
Publication as a Working Draft does not imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or obsoleted
by other documents at any time. It is inappropriate to cite W3C Working Drafts
as other than "work in progress."
Please send comments about this document to the public mailing list firstname.lastname@example.org (public archives).
This document has been produced as part of the Web Accessibility Initiative. The goals of the User Agent Working Group are described in
the charter. A list
of the Working Group
participants is available.
A list of current W3C Recommendations and other technical documents can be
found at http://www.w3.org/TR.
This introduction (section 1) provides context for understanding the
guidelines listed in section 2. In different
sections, the introduction explains:
For those unfamiliar with accessibility issues pertaining to user agent
design, consider that many users with disabilities may be accessing the Web in
contexts very different from your own:
- Users may not be able to see, hear, move, or may not be able to process
some types of information easily or at all.
- Users may have difficulty reading or comprehending text.
- Users may not have or be able to use a keyboard or mouse.
User agents must be designed to take into account the diverse requirements
of users with disabilities. This document specifies requirements that user agent developers must satisfy to ensure
accessibility of the user agent.
Software that follows the guidelines in this document will not only benefit
users with disabilities, it will be more flexible, manageable, extensible, and
beneficial to all users. Many users browse the Web with requirements similar to
those of users with disabilities. For instance:
- They may have a text-only screen, a small screen, or a slow Internet
connection (e.g., via a mobile phone browser). These users will benefit from
the same features that provide access to people with low vision or
- They may be in a situation where their eyes, ears, or hands are busy or
interfered with (e.g., driving to work, working in a noisy environment, etc.).
These users will benefit from the same features that provide access to people
who cannot use a mouse or keyboard due to a visual or physical disability.
- They may not understand fluently the natural language of spoken content.
These users may benefit from the same text
equivalents that make spoken language accessible to people with a
The guidelines in this document describe some basic principles of accessible
design. As the previous examples illustrate, accessible design generally
benefits all users.
This document is organized according to several principles that, if
followed, will improve the design of any type of user agent:
A user with a disability must have access to all the functionalities offered
by the user agent through its user
interface. Since some users cannot use some parts of the user
interface, it needs to be adaptable to their particular needs. To ensure the
accessibility of the user interface, people with disabilities should be
involved in its design and testing.
One requirement is that users be able to operate the user interface with a
variety of input devices (mouse, keyboard, speech input, etc.) and output
devices (graphical display, speech
output, Braille display, etc.). Redundant input and output methods
(accomplished through the standard input and output Application Programming
implemented by the user agent) help users operate controls of the user agent as
well as those included as part of content.
In order for people to use the user agent at all, the installation procedure
(and any subsequent software update procedures) must be accessible according to
the guidelines of this document. For example, the user agent must provide
device-independent access and accessible documentation of the installation.
This document includes a number of user interface requirements that are
similar to, or related to, general guidelines for user interface design. The
general topic of user interface design for computer software exceeds the scope
of this document, though some user interface requirements have been included
because of their importance to accessibility. The Techniques document [UAAG10-TECHS]
includes some references to general software design guidelines and
platform-specific accessibility guidelines.
Note: This document addresses accessible user agent support
for some markup language features (e.g., tables for layout, etc.) that may be
widely deployed, but whose use may be discouraged.
User agents must ensure access to
- By ensuring access to all text, video, sound, and other content, including
for content (e.g., "alt" attribute values in HTML, external long
descriptions, etc.) and relationships among content (e.g., table cells and
- By allowing users to configure
content rendering parameters
(text size, colors, synthesized speech rate and volume, etc.).
- By allowing users to navigate the content (e.g., with scrollbars,
navigation of active elements,
navigation according to structure, etc.).
- By making Web content and user agent information available to assistive technology through
User agents can help the user remain oriented in a page or site by supplying
- Browsing context. This includes information about the number of frames, the
title of the current frame, whether loading for a page or video clip has
finished or stalled, etc. Graphical clues
about browsing context (such as frames, proportional scroll bars, a visually highlighted selection, etc.) help some, but not
all users, so the context information must be available in a device-independent
- Element context. This includes information about specific elements (e.g.,
the dimensions of a table, the length of an audio clip, the structure of a
form, etc.) and surrounding information. For instance, users who are blind and
who may navigate by jumping from link to link on a page or presentation will
benefit from nearby information that helps them decide quickly whether to
follow the link, as well as from metadata about the link: whether it has been
visited, the type of the target resource, the length of an audio or video clip
that will be started, whether activating the link involves a fee, etc.
The user agent should also minimize chances that user will become
disoriented. User agents should:
- For changes to the content or viewport that the user does not initiate, allow the
user to request notification when these changes occur (e.g., when a viewport
opens, a script is executed, etc.).
- Allow the user to return to a known state (e.g., by providing browsing
Following platform and operating system standards and guidelines promotes
accessibility, usability, and predictability. Platform guidelines explain what
users will expect from the look and feel of the user interface, keyboard
conventions, documentation, etc. Platform guidelines also include information
about accessibility features that the user agent should adopt rather than
So that desktop browsers can make information available to assistive technologies, they
must communicate through standard interfaces. An architecture that makes
possible programmatic access to content and the
user interface will benefit
assistive technologies, scripting tools, and automated test engines. It will
also promote software modularity and reuse.
The eleven guidelines in this document state general principles for the
development of accessible user agents. Each guideline includes:
- The guideline number.
- The statement of the guideline.
- The rationale behind the guideline and identification of some groups of
users who benefit from it.
- A list of checkpoint definitions. This list may be split into groups of
related checkpoints. For instance, the list might be split into one group of
"checkpoints for content accessibility" and a second group of "checkpoints for
user interface accessibility". Within each group, checkpoints are ordered
according to their priority, e.g., Priority 1 before
Each checkpoint definition includes:
- The checkpoint number.
- The statement of the checkpoint.
- The priority of the checkpoint.
- Optional informative notes, clarifying examples, and cross references to
related guidelines or checkpoints. Note: Some checkpoints in
this document are more general than others, and some may overlap in scope.
Special case checkpoints that identify important accessibility requirements are
- A link to a corresponding section of "Techniques for User Agent
Accessibility Guidelines 1.0" [UAAG10-TECHS], where the checkpoint is examined in
detail, including information about implementation and examples.
Each checkpoint is intended to be specific enough so that someone reviewing
a user agent may verify that the checkpoint has been satisfied.
Note: The checkpoints have been designed to be verifiable, although
some may be difficult to verify without documentation from vendors about what
features and APIs they
This document includes as an appendix a glossary. Another appendix lists all
checkpoints in tabular and linear format for convenient reference
A separate document, entitled "Techniques for User Agent Accessibility
Guidelines 1.0" [UAAG10-TECHS], provides suggestions and examples of how each
checkpoint might be satisfied. It also includes references to other
accessibility resources (such as platform-specific software accessibility
guidelines) that provide additional information on how a user agent may satisfy
each checkpoint. Readers are strongly encouraged to become familiar with the
Techniques document. Note that the techniques provided are informative examples
only, and other strategies may be used to meet the checkpoint as well as, or in
place of, those listed therein. The Techniques document is expected to be
updated more frequently than the current guidelines.
"User Agent Accessibility Guidelines 1.0" is part of a series of
accessibility guidelines published by the Web
Accessibility Initiative (WAI). The series also includes "Web Content Accessibility
[WCAG10] and "Authoring Tool Accessibility Guidelines 1.0" [ATAG10]. In addition to
this series, WAI
provides other resources and educational materials about Web accessibility.
The following editorial conventions are used throughout this document:
element names are in uppercase letters
(e.g., H1, BLOCKQUOTE, TABLE, etc.)
- HTML attribute names are
double-quoted in lowercase letters (e.g., "alt", "title", "class", etc.)
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.
This section explains how to make a valid
claim that a user agent conforms to this document. The terms "must",
"should", and "may" (and related terms) are used in this document in accordance
with RFC 2119
Anyone may make a claim (e.g., vendors about their own products, third
parties about those products, journalists about products, etc.). Claims may be
published anywhere (e.g., on the Web or in product documentation).
Claimants are solely responsible for their claims and the use of the conformance icons. If the subject of the claim
(i.e., the software) changes after the date of the claim, the claimant is
responsible for updating the claim. Claimants are encouraged to conform to the
most recent guidelines available.
This document has been designed to promote the accessibility of
general-purpose graphical user agents. While many of the principles set forth
in this document apply to other classes of user
agents, including assistive technologies, many of the checkpoints do not. As
the number of applicable checkpoints decreases for a piece of software, the
likelihood increases that the guidelines are not an accurate gauge of the
accessibility of that piece of software. Therefore, while assistive
technologies and other specialized user agents obviously promote accessibility,
they are not expected to conform (for instance, because they target a
particular user group, or they do not make available information through APIs) because they
generally do strive to be general purpose user agents. This document will help
assistive technology developers understand what functionalities and
communication an accessible general purpose user agent should provide.
Note: These guidelines aim to make conforming user agents
accessible. This includes the accessibility of the user agent's user interface
in addition to the accessibility of Web content. When used in conjunction with
assistive technology, conforming user agents are expected to be accessible to
most users with disabilities; in some cases, accessibility is "completed" by
the use of an assistive technology. Some user agents may not conform to these
guidelines but still be accessible to some users with disabilities. By
following the principles of this document, developers of all user agents (not
just conforming user agents) should improve the accessibility of their
A conformance claim must indicate what conformance level is met:
Note: Conformance levels are spelled out in text (e.g.,
"Double-A" rather than "AA") so they may be understood when rendered as
A well-formed claim must include the following information:
- About the guidelines:
- The guidelines title/version: "User Agent Accessibility Guidelines
- The URI of the guidelines:
- The conformance level satisfied: "A",
"Double-A", or "Triple-A".
- The checkpoints of the chosen conformance level considered not applicable. Claimants may use the checklist
[UAAG10-CHECKLIST] for this purpose.
- About the subject of the claim:
- The vendor name.
- The product name and version information (version number, minor release
number, and relevant bugfix update level).
- The operating system name and version number.
- Properties of the claim:
There is no restriction on the format used to make the claim, except that at
least one representation of the claim must be accessible according to the Web
Content Accessibility Guidelines 1.0 [WCAG10]. For instance, the claim may be marked up using
HTML, or expressed in the Resource Description Framework
[RDF10] Here is an example of a claim expressed in HTML:
<p>On 7 May 2000, this product (version 2.3 on MyOperatingSystem)
conforms to <abbr title="the World Wide Web
Consortium">W3C</abbr>'s "User Agent Accessibility Guidelines 1.0",
http://www.w3.org/WAI/UA/WD-UAAG10-20000507, level Double-A. The <a
href="http://example.com/checkpoints"> list of checkpoints that do not
apply</a> is available online.</p>
A conformance claim is valid for a given
conformance level if:
- The claim is well-formed, and
- The subject of the claim satisfies all the applicable
checkpoints for that level.
Claimants (or relevant assuring parties) are responsible for the validity of
a claim. As of the publication of this document, W3C does not act as an
assuring party, but it may do so in the future, or establish recommendations
for assuring parties.
Claimants are expected to modify or retract a claim if it may be
demonstrated that the claim is not valid. Please note that it is not currently
possible to validate claims completely automatically.
As part of a conformance claim, people may use a conformance icon on a Web
site, on product packaging, in documentation, etc. Each conformance icon
(chosen according to the appropriate conformance
level) must link to the W3C explanation of the icon. The appearance of a
conformance icon does not imply that W3C has reviewed or validated the claim.
An icon must be accompanied by a well-formed
Note: In the event this document becomes a W3C
Recommendation, additional information about the icons and how to use them will
be available at the W3C Web site.
Not every checkpoint or guideline is applicable to every user agent.
Generally, a user agent must adhere to checkpoints that ensure accessibility of
functionalities that it offers to users and it must implement required
functionalities natively. If the user
agent supports keyboard input, it must support accessible keyboard input. If
the user agent supports images, it must ensure access to each image or an
equivalent alternative specified by the author. If a user agent supports style
sheets, it must implement the accessibility features of the style sheet
language. If the user agent supports frames, it must ensure access to frame
alternatives specified by the author. In short, if a user agent offers a
functionality, it must ensure that people with disabilities have access to that
functionality or an equivalent alternative.
Not all user agents support every content type, markup language feature,
input or output device interface, etc. When a content type, feature, or device
interface is not supported, checkpoints with requirements related to it do not
apply to the user agent. Thus, if a user agent supports style sheets at all,
all checkpoints related to style sheet accessibility apply. If a user agent
does not support style sheets at all, the checkpoints do not apply.
The applicability of checkpoints related to markup language features is
determined similarly. If a user agent supports tables, it must support the
accessibility features of the language related to tables (and so on, for
images, frames, video, links, etc.). The Techniques document includes
information about the accessibility features of W3C languages such as
HTML, CSS, and SMIL.
To summarize, a checkpoint (or portion of a checkpoint) applies to a user
agent unless at least one of the following is true:
- It refers solely to an unsupported input or output device interface. Note
that if the device interface is supported at all, it must be supported
accessibly for all functionalities of the user agent (and not just a subset of
- It includes requirements about the purpose of content (e.g., transcript,
caption, text equivalent, etc.) that the user agent cannot recognize through markup. For instance, HTML user
agents can recognize "alt", OBJECT content, or NOFRAMES content as providing
equivalents for other content since these are specified by the markup language.
HTML user agents are not expected to recognize that an image description
embedded in a paragraph is a text equivalent for the image.
- It includes requirements about a content type (script, image, video, sound,
applet, etc.) that the user agent either does not
recognize or recognizes but does not support
- It requires control of properties of an embedded object (e.g., video or
animation rate) that may not be controlled or accessed by the user agent.
- It refers to unsupported technologies that are not required by this
document. For instance, all conforming user agents are required to support the
W3C Document Object Model
[DOM2]. However, user agents are not required to support a
synchronized multimedia markup language such as SMIL 1.0 [SMIL]. If they do, the checkpoints that
refer to synchronized multimedia apply.
- It refers to communication with other software but no communication is
possible on the system housing the user agent (e.g., a kiosk with no infrared
port for communication with assistive
Each checkpoint requirement must be satisfied by making information or
functionalities available through the user agent's user interface unless the checkpoint explicitly
states that the requirement must be met by making information available through
an Application Programming Interface (API).
Since people use a variety of devices for input and output, user agent
developers must ensure redundancy in the user
interface. Messages and alerts to the user must not rely on auditory
or graphical cues alone; text, beeps, flashes, and other techniques used
together will make these alerts accessible. Text messages are generally
accessible since they may be used by people with graphical displays, speech
synthesizers, or Braille displays.
People who cannot or do not use a mouse must be able to operate the user
interface with the keyboard, through voice input, a head wand, touch screen, or
other device. Keyboard operation of all functionalities offered
through the user interface is one of the most important aspects of user agent
accessibility on almost every platform. The keyboard is available to most
users, it is widely supported, and hooks provided for the keyboard can be used
for other types of input.
To ensure that assistive
technologies can both operate the user agent programmatically (e.g.,
through simulated keyboard events) and monitor user agent output (e.g., output
text), developers are expected to use each API appropriately. Developers should not, for
example, pre-rasterize text or convert text to a series of strokes since doing
so may prevent assistive technologies from being able to render the text as
speech or Braille.
Checkpoints for communication with other software:
- 1.1 Ensure that every functionality
available through the user
interface is also available through every input
API implemented by the user agent. [Priority 1]
- Note: This checkpoint does not require developers to
implement all operating system input APIs, only to make the software accessible through
those they do implement. The device-independence required by this checkpoint
applies to the functionalities described by the other checkpoints in this
document (e.g., installation, documentation, user agent user interface configuration, etc.). This
checkpoint does not require developers to reimplement the input methods
associated with the keyboard, pointing device, voice, and other device APIs. For example,
developers are not required to implement text input through a mouse API or
pointer motion through a keyboard API.
- 1.2 Use the standard input
and output device APIs of the operating system. [Priority 1]
- Do not bypass the standard output
APIs when rendering information (e.g.,
for reasons of speed, efficiency, etc.). For example, do not bypass standard APIs to manipulate the
memory associated with rendered
content, since assistive
technologies monitor rendering through the APIs. Note: When available,
developers should use
APIs at a higher level of abstraction than the standard device APIs
for the operating system. If these higher level APIs do not use the standard
device APIs properly, developers should also use the standard device APIs.
1.3 Implement the standard keyboard API of the operating system
and ensure that every functionality available through the user interface is
available through this API.
- Note: This checkpoint always applies on systems with a standard
keyboard API. This checkpoint is an important special case of checkpoint 1.1. Refer also to checkpoint
Checkpoints for user interface accessibility:
- 1.4 Ensure that the user can
interact with all active
elements in a
- For example, users who are blind or have physical disabilities must be able
to activate text links, the links in a client-side
image map, and form controls without a pointing
device. Note: This checkpoint is an important special case of
1.5 Ensure every non-text message (e.g., prompt, alert,
notification, etc.) that is part of the user agent's user interface also has a
text equivalent in the user interface.
- Note: For example, if the user is
notified of an event by an auditory cue, a text equivalent in the status bar
would satisfy this checkpoint. Use standard interface controls so that text
equivalents are available through standard APIs. The text equivalent must be
available to assistive technologies so that it can be rendered visually, as
synthesized speech, or as Braille.
Refer also to checkpoint 5.5.
Just as people use a variety of devices for
user interface input and output, they require that content be available in different modes -- auditory
(synthesized and prerecorded), tactile (Braille),
graphical, or a mix of some of these. Authors and user agents share
responsibility for ensuring redundant modes. Web content providers specify equivalent alternatives for
content, such as text
equivalents for images or video, according to the conventions of the
markup language they are using (refer to the Techniques document [UAAG10-TECHS]
for details). User agents must ensure that users have access to this content,
as well as any alternatives generated by the user agent itself. User agents
should allow users to specify whether primary content should be rendered,
equivalent alternatives should be rendered, or both.
Ensuring access to equivalent alternatives benefits all users since some
users may not have access to some content due to a technological limitation
(e.g., their mobile browser cannot display graphics) or simply a configuration
preference (e.g., they have a slow Internet connection and prefer not to
Checkpoints for content accessibility:
- 2.1 Make all
content available through the user interface. [Priority 1]
- Users must have access to the entire
document object, including equivalent alternatives for
content, attributes, style sheets, etc. through the user interface.
This checkpoint does not require that all content be available in every view. A document source view is part of a solution for
providing access to content, but is not a sufficient solution on its own. Refer
to guideline 5 for more
information about programmatic access to content.
- 2.2 For presentations that require user
input within a specified time interval, allow the user to configure the time interval (e.g., to extend it or to
cause the user agent to pause the presentation automatically and await user
input before proceeding). [Priority 1]
- 2.3 If content
available in a
viewport has equivalent alternatives, provide easy access in
context to the alternatives.
- For example, if an image in an HTML document has text equivalents, provide access to them by
rendering them nearby, allowing the user to configure the user agent to render
them in place of the image, or allowing the user to follow a readily available
link to them.
- 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 auditory and visual tracks. Respect
author-specified synchronization cues during rendering. [Priority 1]
2.5 When the author has not specified a
text equivalent for content as
required by the markup language, make available other author-specified
information about the content (e.g., object type, file name, etc.). [Priority 2]
2.6 When a text equivalent for
content is explicitly empty (i.e., an empty
string), render nothing. [Priority 3]
- 2.7 For author-identified but
unsupported natural languages,
allow the user to request notification of language changes in content.
Some content or behavior specified by the author may make the user agent
unusable or may obscure information. For instance, flashing content may trigger
seizures in people with photosensitive epilepsy, or may make a Web page too
distracting to be usable by someone with a cognitive disability. Blinking can
affect screen reader users, since screen readers (in conjunction with speech
synthesizers or Braille displays) may repeat the text every time it blinks.
Distracting background images, colors, or sounds make make it impossible for
users to see or hear other content.
Dynamically changing Web content may cause problems for some assistive technologies.
Scripts that cause unanticipated changes (viewports that open, automatically redirected or
refreshed pages, etc.) may disorient some users with cognitive
Users may need to turn off these effects in order to have access to content.
A user agent must provide on/off control even when it hands off content (e.g.,
a sound file) to the operating system or to a helper application for rendering;
the user agent is aware of the content type and thus can choose not to render
it. Please also refer to
guideline 4 and guideline
Checkpoints for content accessibility:
- 3.1 Allow the user to turn on and
off rendering of background images.
- 3.2 Allow the user to turn on and
off rendering of background audio.
3.3 Allow the user to turn on and off rendering of video. [Priority 1]
3.4 Allow the user to turn on and off rendering of audio. [Priority 1]
- 3.5 Allow the user to turn on and off
animated or blinking text.
- 3.6 Allow the user to turn on and off
animations and blinking images.
3.7 Allow the user to turn on and off support for scripts and
applets. [Priority 1]
- Note: This is particularly important for scripts that
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.
- 3.8 For automatic content changes specified by the author (e.g.,
redirection and content refresh), allow the user to slow the rate of change.
3.9 Allow the user to turn on and off rendering of images. [Priority 2]
Providing access to content (refer to guideline 2) includes enabling users to
configure its presentation. Users with low vision may require larger
text than the default size specified by the author or the user agent. Users
with color blindness may need to impose or prevent certain color combinations.
Users with physical or cognitive disabilities may need to configure the rate of
a multimedia presentation.
For dynamic presentations such as synchronized multimedia presentations
created with SMIL 1.0
[SMIL], users with cognitive, hearing, visual, and physical disabilities
may not be able to interact with a presentation within the time delays assumed
by the author. To make the presentation accessible to these users, user agents
rendering synchronized multimedia presentations or audio presentations must
provide access to content in a time-independent manner and/or allow users to
adjust the playback rate of the presentation.
User agents must also allow users to configure the style of the user
interface elements, such as styles for selection
and content focus (e.g., to ensure
adequate color contrast).
For more information about configuration, refer to guideline 10.
Note: The checkpoints in this guideline apply to all
content, including equivalent
Checkpoints for fonts and colors:
- 4.1 Allow the user to configure the size of text.
- For example, allow the user to specify a font size
directly through the user agent user
interface or in a user style
sheet. Or, allow the user to zoom or magnify content.
- 4.2 Allow the user to configure font family.
- 4.3 Allow the user to configure foreground color.
- 4.4 Allow the user to configure background color.
Checkpoints for multimedia and audio presentations:
4.5 Allow the user to slow the presentation rate of audio, video,
and animations. [Priority 1]
- Refer also to
- 4.6 Allow the user to start, stop, pause,
advance, and rewind audio, video, and animations.
- 4.7 Allow the user to position
text transcripts, collated text
transcripts, and captions on graphical displays.
- The user agent is expected to allow the user the same
range of positions that is available to the author according to
- 4.8 Allow the user to configure the audio volume.
Checkpoints for synthesized speech:
- 4.9 Allow the user to configure synthesized speech playback rate. [Priority 1]
- 4.10 Allow the user to configure synthesized speech volume. [Priority 1]
- 4.11 Allow the user to configure synthesized speech pitch, gender, and other
Checkpoints for user interface accessibility:
- 4.12 Allow the user to select from
available author and user style sheets or to ignore them. [Priority 1]
- Note: By definition, the user agent's default style sheet is always present,
but may be overridden by author or user styles.
- 4.13 Allow the user to configure how the
selection is highlighted
(e.g., foreground and background color).
- 4.14 Allow the user to configure how the
content focus is highlighted
(e.g., foreground and background color).
- 4.15 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]
4.16 Allow the user to configure
the user agent to limit the number of open
viewports. [Priority 2]
- Some users may become disoriented when there are too many open viewports.
Refer also to checkpoint
4.15, checkpoint 5.5, and checkpoint
Part of user agent accessibility involves communication within the user's
"accessibility environment." This includes:
- exchanging information about content and user agent user interface controls with other user
agents, especially with assistive
- using standard communication channels for this exchange.
- ensuring the exchange takes place in a timely manner. Otherwise, assistive
technology rendering or response may lag behind that of the "source" user
agent, which can disorient the user. Timely exchange is also necessary for
proper synchronization of alternative renderings and simulation of events.
- following system conventions for user agent
user interface design,
documentation, and installation.
- incorporating system-level user preferences into the user agent. For
instance, some operating systems include settings that allow users to request
high-contrast colors (for users with low vision) or graphical rendering of
audio cues (for users with hearing disabilities).
APIs and following system conventions increases predictability for
users and for developers of assistive
Checkpoints for communication with other software:
5.1 Provide programmatic read access to HTML and
XML content by conforming to the
W3C Document Object Model (DOM) Level 2 Core and HTML modules and
exporting the interfaces they define.
- Note: These modules are defined in DOM
Level 2 [DOM2], chapters
1 and 2. Please refer to that specification for information about which
versions of HTML and XML are supported
and for the definition of a "read-only" DOM. This checkpoint
is an important special case of checkpoint 2.1. For content other than HTML and XML, refer to checkpoint 5.3.
- 5.2 If the user can modify
HTML and XML content through the user interface, provide the same functionality
programmatically by conforming to the W3C Document Object Model (DOM) Level 2 Core and
HTML modules and exporting the interfaces they define. [Priority 1]
- For example, if the user interface allows users to
complete HTML forms, this must also be possible through the
APIs. Note: These modules are defined in DOM Level
2 [DOM2], chapters 1 and
2. Please refer to DOM Level 2 [DOM2] for information about which versions of
HTML and XML are supported. This
checkpoint is an important special case of checkpoint 2.1. For markup languages other than HTML and
XML, refer to checkpoint
- 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]
- Note: This checkpoint addresses content
not covered by checkpoints
checkpoint 5.1 and
checkpoint 5.2. This checkpoint is an important special case of checkpoint 2.1.
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
for the operating system, and conventions for programming languages, plug-ins,
virtual machine environments, etc.)
- 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.
5.5 Provide programmatic notification of changes to content and user
interface controls (including
focus, and user interface
focus). [Priority 1]
- Use the standard APIs required by guideline 5.
5.6 Ensure that programmatic exchanges proceed in a timely manner.
- 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.
5.7 Provide programmatic access to Cascading Style Sheets
(CSS) by conforming to the W3C Document Object Model
(DOM) Level 2
CSS module and exporting the interfaces it defines. [Priority 3]
- Note: This module is defined in DOM
Level 2 [DOM2], chapter
5. Please refer to that specification for information about which versions of
CSS are supported. This checkpoint is an important special
case of checkpoint
Checkpoints for user interface accessibility:
5.8 Follow operating system conventions that affect accessibility.
In particular, follow conventions for user
interface design, keyboard configuration, product installation, and
documentation. [Priority 2]
- Note: Operating system conventions that affect
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
Developers should implement open and accessible specifications. Conformance
to open specifications promotes interoperability and accessibility by making it
easier to design assistive
technologies (also discussed in guideline 5).
While developers should implement the accessibility features of any
specification, this document promotes W3C specifications for several
- W3C specifications include "built-in" accessibility features.
- W3C specifications undergo early review to ensure that accessibility issues
are considered during the design phase. W3C encourages the public to review and
comment on specifications at all times during their development, from Working
Draft to Candidate Recommendation (for implementation experience) to Proposed
- W3C specifications are developed in a consensus process that includes
stakeholders in accessibility. Refer to the process defined by the W3C Process
[W3CPROCESS]. For information about how specifications become W3C
Recommendations, refer to The W3C
Recommendation track ([W3CPROCESS], section 6.2). W3C Recommendations (and other technical reports) are published at the W3C Web
Checkpoints for content accessibility:
- 6.1 Implement the accessibility
features of supported specifications (markup languages, style sheet languages,
metadata languages, graphics formats, etc.).
- Note: This checkpoint applies to all specifications, not
just W3C specifications. The Techniques document [UAAG10-TECHS] provides information
about the accessibility features of some specifications, including W3C
- 6.2 Use and conform to W3C Recommendations
when they are available and appropriate for a task.
- For instance, for markup, implement
[HTML4], XHTML 1.0 [XHTML10], or XML 1.0 [XML]. For style sheets, implement
mathematics, implement MathML [MATHML]. For synchronized multimedia, implement
[SMIL]. For information about programmatic access to
HTML and XML content, refer to guideline 5.
- Note: For reasons of backward
compatibility, user agents should continue to implement deprecated features of
specifications. The current guidelines refer to some deprecated language
features that do not necessarily promote accessibility but are widely deployed.
Information about deprecated language features is generally part of the
Providing a variety of navigation mechanisms helps users with disabilities
(and all users) access content more quickly. Content navigation is particularly
important to users who access content serially (e.g., as synthesized speech or
Sequential navigation (e.g., line scrolling, page scrolling, sequential
navigation through active elements, etc.) means advancing (or rewinding)
through rendered content in well-defined steps (line by line, screen by screen,
link by link, etc.). Sequential navigation can provide context, but can be
time-consuming. Sequential navigation is important to users who cannot scan a
page visually for context and benefits all users unfamiliar with a page.
Sequential access may be based on element type (e.g., links only), content
structure (e.g., navigation from heading to heading), or other criteria.
Direct navigation (go to a particular link or paragraph, search for
instances of a string, etc.) is faster than sequential navigation, but
generally requires familiarity with the content. Direct navigation is important
to users with some physical disabilities (who may have little or no manual
dexterity and/or increased tendency to push unwanted buttons or keys) and
benefits all "power users." Selecting text or structured content with the
pointing device is another form of direct navigation. Searching on text is one
important variant of direct navigation.
Structured navigation mechanisms such as navigation of headings, tables,
lists, etc., offer both context and speed. Structured access. For information
about programmatic access to document structure, refer to guideline 5.
User agents should allow users to configure navigation mechanisms (e.g., to
allow navigation of links only, or links and headings, or tables and forms,
etc.). For more information about configuration, refer to guideline 10.
Checkpoints for user interface accessibility:
7.1 Allow the user to navigate among
viewports (including frames).
- 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.
Navigating into a viewport makes it the
- 7.2 For user agents that offer a
browsing history mechanism, when the user returns to a previous viewport,
restore the point of regard in the
- For example, when users navigate "back" and "forth"
among viewports, they should return to the same position they left in the
7.3 Allow the user to navigate all
- Navigation may include non-active elements in addition
to active elements. Note: This checkpoint is an important
special case of checkpoint
7.4 Allow the user to choose to navigate only active elements.
7.5 Allow the user to search for rendered text content, including rendered text equivalents.
- Note: Use operating system conventions for marking the
result of a search (e.g., selection or
7.6 Allow the user to navigate efficiently to and among important
structural elements identified by the author.
- Structured navigation of headings, tables, forms, lists, etc. is most
effective when available in conjunction with a configurable view (checkpoint 8.4 and checkpoint 8.5). Users should
be able to navigate to important pieces of content within a configurable view,
identify the type of object they have navigated to, interact with that object
easily (if its an active element), and recall the surrounding context (orient
themselves). Use operating system conventions to indicate navigation progress
- 7.7 Allow the user to configure structured navigation. [Priority 3]
- For example, allow the user to navigate only paragraphs, or only headings
and paragraphs, etc.
All users require clues to help them understand their "location" when
browsing. Some mechanisms that provide such clues include:
- Highlighted (either graphically or aurally)
selection and content
focus mechanisms, which distinguish the selected or focused content
from other content.
- A history mechanism, which allows users to return to a familiar or
Orientation mechanisms such as these are especially important to users who
view content serially, (e.g., when rendered as speech or Braille). For
instance, these users cannot "scan" a graphically displayed table with their
eyes for information about a table cell's headers, neighboring cells, etc. User
agents must provide other means for users to understand table cell
relationships, frame relationships (what relationship does the graphical layout
convey?), form context (have I filled out the form completely?), link
information (have I already visited this link?), etc.
User agents must make orientation information available in an output device
independent manner. Refer also
to guideline 1.
Checkpoints for content accessibility:
8.1 Make available to the user the author-specified purpose of each
table and the relationships among the table cells and headers. [Priority 1]
- For example, provide information about table headers, how headers relate to
cells, table summary information, cell position information, table dimensions,
etc. Graphical user agents may satisfy this checkpoint by rendering a table as
a two dimensional grid and by ensuring that users can find headers associated
with cells. Refer also to
checkpoint 5.3. Note: This checkpoint is an important
special case of checkpoint
- 8.2 Indicate to the user whether a link has
been visited. [Priority 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
8.3 Indicate to the user whether a link has been marked up to
indicate that following it will involve a fee.
- Note: This checkpoint is an important
special case of checkpoint 8.6.
The W3C specification "Common Markup for micropayment per-fee-links" [MICROPAYMENT]
describes how authors may mark up micropayment information in an interoperable
- 8.4 Make available to the user an
"outline" view of content, built from structural
elements (e.g., frames, headings, lists, forms, tables, etc.). [Priority 2]
- 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.
Note: This checkpoint does not require that the outline view
be navigable, but this is recommended (refer to checkpoint 7.6).
- 8.5 Allow the user to configure the
outline view. [Priority 3]
- For example, allow the user to configure
the level of detail of the outline. Refer also to checkpoint 8.4 and checkpoint 5.4.
8.6 To help the user decide whether to follow a link, make available
link information specified by the author and computed by the user agent. [Priority 3]
- Information specified by the author includes link
content, link title, whether the link is internal, whether it involves a fee,
and hints on the content type, size, or natural language of the linked
resource. Information computed by the user agent includes whether the user has
already visited the link. Note: User agents are not required
to retrieve the resource designated by a link as part of computing information
about the link.
- 8.7 Allow the user to configure what
information about links to present.
- Note: Refer also to checkpoint 8.6.
Checkpoints for user interface accessibility:
- 8.8 Implement selection,
content focus, and user interface
- Follow system conventions for these mechanisms, per checkpoint 5.8. Refer also to checkpoint 7.1.
- 8.9 Provide a mechanism for highlighting and identifying (through a
standard interface where available) the current
viewport, selection, and content focus.
- Note: This includes highlighting and
identifying frames. Note: This checkpoint is an important
special case of checkpoint
1.1. Refer also to checkpoint
- 8.10 Provide a mechanism for highlighting and identifying active elements.
- On most systems, the focus is used
to identify and highlight active elements.
For people with visual disabilities or certain types of learning
disabilities, it is important that the
point of regard remain as stable as possible. Unexpected changes may
cause users to lose track of how many viewports
are open, which is the current viewport, etc. User agents should notify the
user of content and viewport changes caused by scripts, or allow users to turn
off scripts entirely (refer to
Refer to checkpoint 5.5 for
requirements about notification of user interface changes through an API.
Checkpoints for user interface accessibility:
- 9.1 Ensure that when the selection or
content focus changes, it is in a
viewport after the change.
- For example, if users navigating links move to a portion
of the document outside the viewport, the viewport should scroll to include the
new location of the focus.
- 9.2 Allow configuration so the user is
prompted to confirm any form submission not caused by explicit activation of a
form submit control. [Priority 2]
- 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
- 9.3 Allow the user to configure
notification preferences for common types of
content and viewport changes. [Priority 3]
- For example, allow the user to choose to be notified (or
not) that a script has been executed, that a new
viewport has been opened, that a pulldown menu has been opened, that
a new frame has received focus, etc.
- 9.4 When transferring content (e.g., a document, image, audio, video, etc.)
indicate what proportion of the content has been transferred and whether the
transfer has stalled. [Priority 3]
- 9.5 Indicate the relative position of the viewport in
rendered content (e.g., the percentage of an audio or video clip
that has been played, the percentage of a Web page that has been viewed, etc.).
- Note: The user agent may calculate the
percentage according to content focus position, selection position, or viewport
position, depending on how the user has been browsing.
Web users have a wide range of capabilities and must be able to configure the user agent according to their
preferences for styles, graphical user interface configuration, keyboard
Checkpoints for user interface accessibility:
- 10.1 Provide information to the user
about current user preferences for input configurations (e.g., keyboard or voice
bindings). [Priority 1]
- 10.2 Avoid default input configurations that
interfere with operating system accessibility conventions. [Priority 1]
- In particular, default configurations should not
interfere with operating conventions for keyboard accessibility. Information
about operating system accessibility conventions is available in the Techniques
[UAAG10-TECHS]. Refer also to
- 10.3 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]
10.4 Allow the user to change the input configuration.
- For voice-activated browsers, allow the user to modify
which voice commands activate functionalities. Similarly, allow the user to
modify the graphical user agent user
interface for quick access to commonly used functionalities (e.g.,
through buttons). Refer also to checkpoint 10.5 and checkpoint 10.9.
- 10.5 Allow the user to configure the user agent so that the user's preferred
one-step operations may be activated with a single input command (e.g., key
stroke, voice command, etc.).
- Note: User agents are not required to provide single
command activation of all user agent functionalities at once, only some of
them. Furthermore, in some modes of interaction (e.g., when the user is
entering text), the number of single commands available will be significantly
reduced. This checkpoint is an important special case of checkpoint 10.4.
- 10.6 Follow operating system
conventions to indicate the input
configuration. [Priority 2]
- 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. Note: This checkpoint is an important special case
of checkpoint 5.8.
10.7 For the configuration requirements of this document, allow the
user to save user preferences in a profile. [Priority 2]
- Note: This includes user preferences
for styles, presentation rates, input configurations, navigation, viewports, and
notification. Users must be able to select from among available profiles or no
profile (i.e., the user agent default settings).
- 10.8 Ensure that frequently used
functionalities are easily activated in the default input configuration. [Priority 3]
- Make the most frequent operations easy to access and operable through a
- 10.9 For graphical user interfaces, allow
the user to configure the arrangement of
user agent user interface
controls. [Priority 3]
- For instance, allow users to configure which of available controls appear
on a graphical tool bar. Note: This checkpoint is an important
special case of checkpoint
anything that explains how to install, get help for, use, or configure the
product. At least one version of the documentation must conform to the Web
Content Accessibility Guidelines 1.0 [WCAG10].
Features that support accessibility must be clearly documented so that users
with disabilities can learn to operate the user agent efficiently.
Documentation of keyboard accessibility is particularly important to users with
visual disabilities and some types of physical disabilities. Without this
documentation, a user with a disability (or multiple disabilities) may not
think that a particular task can be performed. Or the user may try to use a
much less efficient technique to perform a task, such as using a mouse, or
using an assistive technology's mouse emulation key strokes.
Refer also to checkpoint
Checkpoints for accessible documentation:
11.1 Provide a version of the product
documentation that conforms to the Web Content Accessibility
[WCAG10]. [Priority 1]
- User agents may provide documentation in many formats,
but at least one must conform to the Web Content Accessibility Guidelines 1.0
Document all user agent features that promote accessibility. [Priority 1]
- For example, review the documentation or help system to
ensure that it includes information about the accessibility features discussed
in this document.
Document the default input configuration (e.g., default keyboard
bindings). [Priority 1]
- 11.4 In a dedicated section of the
documentation, describe all features of
the user agent that promote accessibility.
- Note: This is a more specific
- 11.5 In each software release, document all changes that affect accessibility.
- Note: Features that affect accessibility are listed in
this document and in platform-specific accessibility guidelines.
- 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). Which elements are
active depends on the document language and whether the features are supported
by the user agent. In HTML 4.01 [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 resource. When a form control is activated, it
may change state (e.g., check boxes) or may take user input (e.g., a text
field). Refer also to the definition of event
- Application Programming
- An application programming interface (API) defines how communication
may take place between applications.
- In the context of this document, an assistive technology
user agent that:
- relies on services (such as retrieving 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),
For example, screen reader software is an assistive technology because it
relies on browsers or other application 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
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
- speech recognition software, which may be used by people who have some
- 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.
- 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
- An audio presentation is a stand-alone audio track. Examples of audio
presentations include a musical performance, a radio-style news broadcast, and
a book reading. When an audio presentation includes natural language, one can
create a text equivalent for it (e.g., a
- 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 auditory track of the presentation, usually during
natural pauses in the auditory track. Auditory descriptions include information
about actions, body language, graphics, and scene changes.
- Authors styles are style property values that come from a
document, its associated style sheets, or are generated by the server.
- Captions (or sometimes "closed captions") are
text transcripts that are synchronized
with other auditory 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.
- 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 auditory 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.
- In the context of this document, to configure means to
choose, from a set of options, preferences for interface layout, user agent
behavior, rendering style, and other parameters required by this document. This
may be done through the user agent's user
interface, through profiles, style
sheets, by scripts, etc. Users should be able to save their configurations
across user agent sessions (e.g., in a profile).
The range of available configurations (e.g., colors, font families and sizes,
sound quality, etc.) may depend on system or hardware limitations.
- In this specification, the term "content" is used in two
- Content refers to the document
object as a whole or in parts. Phrases such as "content type", "text
content", and "language of content" refer to this usage. When used in this
sense, the term content encompasses
equivalent alternatives. Refer also to the definition of
rendered content. and other accessibility
- Content refers to 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.
- In this document, the noun "control" means "user interface
component" or "form component".
- Device-independence refers to the ability to make use of
software with any supported input or output device. User agents should follow
operating system conventions and use standard system APIs for input and output.
Object, Document Object
- The document object is 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.) or produced as a result of
preferences set within the user agent. 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 invisibly by the user agent, 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 will vary in implementation and sometimes in scope.
Nevertheless, this document calls for developers of user agents to adhere the
W3C Document Object Model
(DOM), which specifies a standard interface
for accessing HTML and XML content. This standard interface allows authors to
a consistent manner across different scripting languages. As a standard
interface, use of a W3C DOM makes 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. The relevant W3C DOM
Recommendations are listed in the references. In this
specification, the acronym "DOM" refers to the W3C DOM.
- 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
resource on the Web. A document source view represents all or part of a
document in a way that exposes the markup language(s) used to build the
resource. A source view often presents textual representations of content.
Refer also to the definition of content.
- Documentation refers to all information
provided by the vendor about a product, including all product manuals,
installation instructions, the help system, and tutorials.
- This document uses the term "element" both in the XML
sense (an element is a syntactic construct as described in the XML 1.0
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 alternatives for
- Since content in some
forms is not always accessible to users with disabilities, authors must provide
equivalent alternatives for inaccessible content. In the context of this
document, the equivalent must fulfill essentially the same function for the
person with a disability (at least insofar as is feasible, given the nature of
the disability and the state of technology), as the "primary" content does for
the person without any disability. For example, the text "The Full Moon" might
convey the same information as an image of a full moon when presented to users.
Note that equivalent information focuses on fulfilling the same function. If
the image is part of a link and understanding the image is crucial to guessing
the link target, an equivalent must also give users an idea of the link
- Equivalent alternatives of content include text equivalents (long and short,
synchronized and unsynchronized) and non-text equivalents (e.g., an auditory description, or a
visual track that shows a sign language translation of a written text, etc.).
Please also consult the Web Content Accessibility Guidelines 1.0 [WCAG10] and its associated
Techniques document [WCAG10-TECHS].
- Each markup language defines its own mechanisms for
specifying equivalent alternatives. For instance, in HTML 4.01 [HTML4] or SMIL 1.0 [SMIL], the "alt" attribute
specifies alternative text for many elements. In HTML 4.01, authors may provide
alternatives 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 alternatives, and NOSCRIPT for script alternatives), and in
- Events and scripting, event
- User agents often perform a task when a certain event
occurs, caused by user interaction (e.g., 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 a specific event occurs, such as
document loading and unloading, mouse press or hover events, keyboard events,
and other user interface events. Note: The combination of
HTML, style sheets, the Document Object Model (DOM), and
scripting is commonly referred to as "Dynamic HTML" or DHTML. However, as there
is no W3C specification that formally defines DHTML, this document only refers
to event handlers and scripts.
- Focus, content focus, user interface focus, current focus
- The notion of focus refers to two identifying mechanisms
of user agents:
The term "focus" encompasses both types of focus. Where one is meant
specifically in this document, it is identified.
- The "content focus" designates an
active element in a document. A viewport has at most one content
- 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.).
- 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.
- In this document, the term graphical refers to information
(text, graphics, colors, etc.) rendered for visual consumption.
- A highlight mechanism emphasizes selected or focused
content. For example, graphical highlight mechanisms include dotted boxes,
underlining, and reverse video. Synthesized speech highlight mechanisms include
alterations of voice pitch and volume.
- 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 included in the user agent
- A user agent supports a feature natively if it does not
require another piece of software (e.g., plug-in or external program) for
support. Operating system features adopted as part of the user agent are
considered part of native support. However, since the user agent is responsible
for the accessibility of native features, it is also considered responsible for
the accessibility of adopted operating system features.
- 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 4.01 ([HTML4] section 8.1), the "xml:lang" attribute
in XML 1.0 ([XML], section 2.12), the
HTML 4.01 "hreflang" attribute for links in HTML 4.01
12.1.5), the HTTP Content-Language header ([RFC2616], section 14.12) and the Accept-Language
request header ([RFC2616], section 14.4).
- Point of
- The point of regard of a
viewport is its position in
rendered content. What is meant precisely by "the point of regard"
may vary since users may be viewing rendered content with browsers that render
in various ways (graphically, as speech, as
Braille, etc.). Depending on the user agent and browsing context, it may refer
to a two dimensional area (e.g., for graphical rendering) or a single point
(e.g., for aural rendering or voice browsing). The point of regard may also
refer to a particular moment in time for content that changes over time (e.g.,
an audio 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
- 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, etc. On systems with distinct user accounts,
profiles enable users to reconfigure software quickly when they log on, and
they may be shared by several users. Platform-independent profiles are useful
for those who use the same user agent on different platforms.
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 speakers, 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
- A user agent is said to recognize markup, content types,
or rendering effects when it can identify the information. Recognition may
occur through built-in mechanisms, Document Type Definitions (DTDs) style sheets, HTTP headers, and
other means. An example of failure of recognition is that
HTML 3.2 user agents may not recognize the new elements or attributes
of HTML 4.01 [HTML4].
While a user agent may recognize blinking content specified by elements or
attributes, it may not recognize blinking in an applet. The Techniques document
[UAAG10-TECHS] lists some markup known to affect accessibility that should
be recognized by user agents.
- The rendered content is that part of content rendered in a given viewport (whether
graphical, auditory, or tactile).
- 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
- Standard device
- Operating systems are designed to be used by default with
devices such as pointing devices, keyboards, voice input, etc. The operating
system (or windowing system) provides "standard APIs" for these devices. 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
- A text transcript is a text equivalent of audio
information (e.g., an audio
presentation or the auditory 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.
- A user agent is an application that retrieves and renders
Web content, including text, graphics, sounds, video, images, and other content
types. A user agent may require additional user agents that handle some types
of content. For instance, a browser may run a separate program or plug-in to
render sound or video. User agents include graphical desktop browsers,
multimedia players, text browsers, voice browsers, and assistive technologies such
as screen readers, screen magnifiers, speech synthesizers, onscreen keyboards,
and voice input software.
- User agent default
- 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] does not specify default styles for XML documents.
[HTML4] does not specify default styles for HTML documents, but the CSS 2
sample default style sheet for HTML 4 based on current practice.
- For the purposes of this document, user interface includes
The document distinguishes them only where required for clarity.
- 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. that are implemented
- User styles are style property values that come from user interface
settings, user style sheets, or other user interactions.
- User-initiated, user
- An action initiated by the user is one that results from
user operation of the user interface. An action initiated by the user agent is
one that results from the execution of a script (e.g., an event handler bound to an event not triggered
through the user interface), from operating system conditions, or from built-in
user agent behavior.
- Views, viewports, and current
- 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 speaker, 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 should 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
The active participants of the User Agent Guidelines Working Group who
produced this document were: James Allan, Denis Anson, Kitch Barnicle, Harvey
Bingham, Dick Brown, Al Gilman, Jon Gunderson, Ian Jacobs, Marja-Riitta
Koivunen, Charles McCathieNevile, Mark Novak, David Poehlman, Mickey Quenzer,
Gregory Rosmaita, Madeleine Rothberg, and Rich Schwerdtfeger.
Many thanks to the following people who have contributed through review and
past participation: Paul Adelson, Olivier Borius, Judy Brewer, Bryan Campbell,
Kevin Carey, 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, Eric Hansen, 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.
For the latest version of any W3C specification please consult the list of
W3C Technical Reports at http://www.w3.org/TR.
- "Authoring Tool
Accessibility Guidelines 1.0", J. Treviranus, C. McCathieNevile, I. Jacobs,
and J. Richards, eds., 3 February 2000. This ATAG 1.0
Recommendation is http://www.w3.org/TR/2000/REC-ATAG10-20000203.
- "CSS, level 1
Recommendation", B. Bos, H. Wium Lie, eds., 17 December 1996, revised 11
January 1999. This CSS 1 Recommendation is
- "CSS, level 2
Recommendation", B. Bos, H. Wium Lie, C. Lilley, and I. Jacobs, eds., 12
May 1998. This CSS 2 Recommendation is
- "Document Object Model (DOM)
Level 2 Specification", L. Wood, A. Le Hors, V. Apparao, L. Cable, M.
Champion, J. Kesselman, P. Le Hégaret, T. Pixley, J. Robie, P. Sharpe,
C. Wilson, eds. The latest version of the specification is available at:
- "HTML 4.01
Recommendation", D. Raggett, A. Le Hors, and I. Jacobs, eds., 24 December
1999. This HTML 4.01 Recommendation is
Markup Language", P. Ion and R. Miner, eds., 7 April 1998. This MathML 1.0
Recommendation is http://www.w3.org/TR/1998/REC-MathML-19980407.
- "Common Markup for
micropayment per-fee-links", T. Michel, ed. The latest version of this W3C
Working Draft is available at http://www.w3.org/TR/Micropayment-Markup.
Description Framework (RDF) Model and Syntax Specification", O. Lassila, R.
Swick, eds., 22 February 1999. This RDF Recommendation is
- "Key words for use in RFCs to
Indicate Requirement Levels", S. Bradner, March 1997.
- "Hypertext Transfer Protocol
-- HTTP/1.1, J. Gettys, J. Mogul, H. Frystyk, L. Masinter, P. Leach, T.
Berners-Lee, June 1999.
Multimedia Integration Language (SMIL) 1.0 Specification", P. Hoschka, ed.,
15 June 1998. This SMIL 1.0 Recommendation is
- An appendix to this document lists all of the checkpoints, sorted by
priority. The checklist is available in either tabular form
- "Techniques for User Agent
Accessibility Guidelines 1.0," J. Gunderson, I. Jacobs, eds. The latest
draft of the techniques document is available at
- World Wide
Web Consortium Process Document, I. Jacobs ed. The 11 November 1999 version
of the Process Document is
- "Web Content
Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, and I. Jacobs,
eds., 5 May 1999. This WCAG 1.0 Recommendation is
- "Techniques for Web Content
Accessibility Guidelines 1.0", W. Chisholm, G. Vanderheiden, and I. Jacobs,
eds. The latest version of this document is available at
- "XHTML[tm] 1.0: The
Extensible HyperText Markup Language", S. Pemberton, et al. The 26 January
2000 XHTML 1.0 Recommendation is
- "Extensible Markup
Language (XML) 1.0.", T. Bray, J. Paoli, C.M. Sperberg-McQueen, eds., 10
February 1998. This XML 1.0 Recommendation is