User Agent Accessibility Guidelines 1.0

Abstract

This document provides guidelines for designing user agents that lower barriers to Web accessibility for people with disabilities (visual, hearing, physical, and cognitive). User agents include HTML browsers and other types of software that retrieve and render Web content. A user agent that conforms to these guidelines will promote accessibility through its own user interface and through other internal facilities, including its ability to communicate with other technologies (especially assistive technologies). By following these guidelines, developers will create more usable software for all Web users.

In addition to helping developers of HTML browsers, media players, etc., this document will also benefit developers of assistive technologies because it explains what types of information and control an assistive technology may expect from a conforming user agent. Technologies not addressed directly by this document (e.g., technologies for braille rendering) will be essential to ensuring Web access for some users with disabilities.

Status of this document

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 version of the document incorporates UAWG resolutions to some issues raised during the second last call. This document includes some changes not yet agreed on by the Working Group, and does not yet address all issues raised during last call.

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."

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.

Related resources

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. The techniques provided in "Techniques for User Agent Accessibility Guidelines 1.0" are informative examples only, and other strategies may be used or required to satisfy the checkpoints. The Techniques document is expected to be updated more frequently than the current guidelines.

The Web Accessibility Initiative provides other resources and educational materials to promote Web accessibility. Resources include information about accessibility policies, links to translations of WAI materials into languages other than English, information about specialized user agents and other tools, accessibility training resources, and more.

1. Introduction

This document specifies requirements that user agent developers must satisfy to lower barriers to accessibility. This introduction (section 1) provides context for understanding the guidelines listed in section 2. Section 1 explains the relationship of this document to other accessibility guidelines published by the Web Accessibility Initiative, which user agents are expected to conform, known limitations of this document, and the relationship of this document to other software design guidelines. Section 3 explains how to make claims that software conforms to these guidelines and details about the applicability of the requirements for different kinds of user agents.

1.1 Relationship to WAI accessibility guidelines

"User Agent Accessibility Guidelines 1.0" (UAAG 1.0) is part of a series of accessibility guidelines published by the Web Accessibility Initiative (WAI). The documents in this series reflect an accessibility model in which Web content authors, format designers, and software developers have roles in ensuring that users with disabilities have access to the Web. These roles intersect as follows:

• Protocol (e.g., HTTP) and content format (e.g., HTML, XML, SVG, etc.) specifications allow communication on the Web. These specifications includes features that authors may use to create accessible content, and features that user agents must support through an accessible user interface. For instance, authors must provide accessible alternatives to inaccessible content, and user agents must allow users to access these alternatives.
• Authors make use of the accessibility features of different format specifications, they use markup appropriately, they write in clear and simple language, organize a Web site consistently, etc. The "Web Content Accessibility Guidelines 1.0" [WCAG10] explains the responsibilities of authors in meeting the needs of users with disabilities. In User Agent Accessibility Guidelines 1.0, WCAG 1.0 is considered the reference for what defines accessible Web content. The "Authoring Tool Accessibility Guidelines 1.0" [ATAG10] explains the responsibilities of authoring tool developers. An accessible authoring tool facilitates the creation of accessible Web content and may be operated by users with disabilities.
• User agent developers design software that conforms to specifications (including implementation of their accessibility features), provides an accessible user interface, accessible documentation, and communicates with other software (notably assistive technologies).

This document explains the responsibilities of user agents in meeting the needs of users with disabilities. The requirements of this document interact with those of the "Web Content Accessibility Guidelines 1.0" [WCAG10] in a number of ways:

• UAAG 1.0 checkpoint 6.1 requires implementation of the accessibility features of all implemented specifications. Features are those identified as such and those that satisfy all of the requirements of WCAG 1.0 [WCAG10].
• UAAG 1.0 checkpoint 10.1 requires conformance to WCAG 1.0 for user agent documentation.
• UAAG 1.0 also incorporates some terms and concepts from WCAG 1.0, a natural consequence of fact that the documents were designed to complement one another.

Formats, authors, and designers all have limitations. No format allows authors to encode all of their knowledge in a way that a user agent can recognize. A format may lack features required for accessibility. An author may not make use of the accessibility features of a format or may misuse a format (which can cause problems for user agents). A user agent designer may not implement a format specification correctly or completely. Some requirements of this document take these limitations into account.

• UAAG 1.0 includes requirements to satisfy the expectations set by WCAG 1.0 "until user agent" clauses. These clauses make additional requirements of authors in order to compensate for some limitations of deployed user agents.
• UAAG 1.0 includes several repair requirements (e.g., checkpoints checkpoint 2.6 and checkpoint 2.8) for cases where content does not conform to WCAG 1.0. Some requirements in this document support authoring practices that may be widely deployed but that are discouraged because they cause accessibility or usability problems (e.g., some uses of HTML frames).
• Except for the indicated repair checkpoints, UAAG 1.0 only requires user agents to handle what may be recognized through protocols and formats. For example, user agents are not expected to recognize that the author has used "clear and simple" language to express ideas. Please see the section on checkpoint applicability for more information about what the user agent is expected to recognize.

1.2 Target user agents

This document was designed specifically to improve the accessibility of mainstream user agents with multimedia capabilities for users with one or more disabilities (visual, hearing, physical, and cognitive). In this context, a mainstream user agent is one designed for the general public to handle general-purpose content in ordinary operating conditions. It is expected that a conforming user agent will typically consist of a Web browser, one or more media players, and possibly other components.

A user agent that conforms to these guidelines will enable access through its own user interface and through other internal facilities, including its ability to communicate with other technologies (especially assistive technologies). Technologies not addressed directly by this document (e.g., those for braille rendering) will be essential to ensuring Web access for some users with disabilities. Note that the ability of conforming user agents to communicate well with assistive technologies will depend in part on the willingness of assistive technology developers to follow the same standards and conventions for communication.

This document allows a certain amount of flexibility in the features a user agent must support in order to conform. For example, some user agents may conform even though they do not support certain content types such as video or audio. For more information about the scope of conformance claims, please see the section on conformance.

1.3 Known limitations of this document

People with (or without) disabilities access the Web with widely varying sets of capabilities, software, and hardware. Some users with disabilities:

• May not be able to see, hear, move, or may not be able to process some types of information easily or at all.
• May have difficulty reading or comprehending text.
• May not have or be able to use a keyboard or mouse.

This document does not include requirements to meet all known accessibility needs. Some known limitations of this document include the following:

• Braille. This document does not address braille rendering.
• Synthesized speech. This document includes only three checkpoints related to synthesized speech (checkpoints 4.11, 4.12 and 4.13).
• Size and color of non-text content. This document includes some checkpoints to ensure that the user is able to control the size and color of visually rendered text content (checkpoints 4.1 and 4.3). This document does not in general address control of the size and color of visually rendered non-text content. Note: Resizing capabilities may be required for conformance to other specifications (e.g., SVG [SVG]).
• Input modalities. This document only includes requirements for keyboard, pointing device, and voice input modalities. This document includes several checkpoints related to voice input as part of general input requirements (e.g., use of standard APIs and configurability of voice input). This document does not otherwise address voice-based navigation or control. Note: The UAWG intends to coordinate further work on the topics of voice input and synthesized speech output with groups in W3C's Voice Browser Activity.
• Time. This document includes requirements for control of some time parameters (including checkpoint 2.2, checkpoint 4.4, checkpoint 4.5, and checkpoint 4.11). The requirements are for time parameters that the user agent recognizes and controls. This document does not include requirements for control of server-side time parameters.
• Security. This document does not address security issues that may arise as a result of these requirements. For instance, requirements that software be able to read and write content and user interface information through APIs raise security issues. See the section on restricted functionality and conformance.
• Intellectual property. This document does not address intellectual property issues that may arise as a result of these requirements.

1.4 Relationship to general software design guidelines

Considerable effort has been made to ensure that the requirements of this document are compatible with other good software design practices. However, this document does not purport to be a complete guide to good software design. For instance, 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 for User Agent Accessibility Guidelines 1.0" [UAAG10-TECHS] includes some references to general software design guidelines and platform-specific accessibility guidelines (see checkpoint 5.12). To ensure the accessibility of any piece of software, and in particular the user interface, people with disabilities should be involved in its design and testing.

Installation is an important aspect of both accessibility and general software usability. On platforms where a user can install a user agent, the installation (and update) procedures need to be accessible. This document does not include a checkpoint requiring that installation procedures be accessible. Since this document considers installation to be part of software usage, the different aspects of installation (user interface, documentation, system conventions, etc.) are already covered by the complete set of checkpoints.

Benefits of accessible user agent design

Many users without disabilities 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 are likely to benefit from the same features that provide access to people with low vision or blindness.
• 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 are likely to benefit from the same features that provide access to people who cannot use a mouse or keyboard due to a visual, hearing, or physical disability.
• They may not understand fluently the natural language of spoken content. These users are likely to benefit from the same visual rendering of text equivalents that make spoken language accessible to people with a hearing disability.

Software that satisfies the requirements of this document will also be more flexible, manageable, extensible, and beneficial to all users. For example, a user agent architecture that allows programmatic access to content and the user interface will encourage software modularity and reuse, and will enable operation by scripting tools and automated test engines in addition to assistive technologies.

2. The user agent accessibility guidelines

The ten 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 Priority 2.

Each checkpoint definition includes:

• The checkpoint number.
• The statement of the checkpoint. The statement of the checkpoint is one or more requirements that must be satisfied by the user agent (i.e., the "subject of the claim) for the purposes of conformance. The "user agent" may consist of more than one software component, as explained in the section on well-formed conformance claims.
• The priority of the checkpoint.
• Content type labels (zero or more), which may be used in a in conformance claim.
• Informative notes about the checkpoint. These notes do not state requirements that must be satisfied as part of conformance; they are informative only. They are meant to clarify the scope of the checkpoint through further description, examples, cross references, and commentary. Note: Some checkpoints in this document are more general than others, and some may overlap in scope. Therefore, a checkpoint may be identified as an "important special case" of one or more other checkpoints.
• 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 has been designed to express a clear minimal requirement for the purposes of conformance. Both this document and "Techniques for User Agent Accessibility Guidelines 1.0" [UAAG10-TECHS] suggest how user agent developers may surpass the minimal requirements. Note: In some cases, though the requirement of a checkpoint may be clear, without documentation from vendors (e.g., about implemented APIs), it may be difficult to verify that the subject of a conformance claim has satisfied the requirement.

Priorities

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.

Ensure that the user can interact with the user agent (and the content it renders) through all of the input and output APIs used by the user agent.

Since people use a variety of devices for input and output, user agent developers need to ensure redundancy in the user interface. The user has to 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.). The user also requires access to the full benefit of Web content through each of at least three modalities -- visually-displayed text, synthesized speech, and braille. Text content has the accessibility advantage of being available to people who use graphical displays, speech synthesizers, and braille displays.

People who cannot or do not use a mouse have to be able to operate the user interface with the keyboard, through voice input, a head wand, touch screen, or other device. Keyboard operation (using as few keystrokes as possible) 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 specialized input devices may reuse the keyboard API.

To ensure that assistive technologies can both operate the user agent programmatically (e.g., through simulated keyboard events) and monitor user agent output, developers are expected to use each API appropriately. Developers should not, for example, pre-rasterize text (i.e., turn it into a bitmap for rendering rather using the system's text drawing facilities) since doing so may prevent assistive technologies from being able to render the text as speech or braille.

Checkpoints for user interface accessibility:

1.1 Ensure that the user can operate the user agent fully through keyboard input alone, pointing device input alone, and voice input alone. [Priority 1]

Note: For example, ensure that through all three input modalities, the user can interact with active elements, select content, navigate viewports, configure the user agent, access documentation, install the user agent, etc. A user agent may claim conformance to this document without satisfying the pointing device and voice portions of this checkpoint. See the section on input modality labels.

Techniques for checkpoint 1.1

1.2 Ensure that the user can interact with all active elements through keyboard input alone, pointing device input alone, and voice input alone. [Priority 1]

Note: A user agent may claim conformance to this document without satisfying the pointing device and voice portions of this checkpoint. See the section on input modality labels. This checkpoint is an important special case of checkpoint 1.1.

Techniques for checkpoint 1.2

1.3 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]

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. See also checkpoint 5.5.

Techniques for checkpoint 1.3

Ensure that users have access to all content, notably author-specified equivalents such as text equivalents and auditory descriptions.

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 speech and prerecorded audio), tactile (braille), graphical, or a mix of some of these. Authors and user agents share responsibility for ensuring redundant modes. Web content authors specify equivalents, 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 content generated by the user agent itself. User agents should allow users to specify whether content should be rendered, equivalents for that content should be rendered, or both.

Ensuring access to equivalents 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 download images).

Checkpoints for content accessibility:

2.1 Make all content available through the user interface. [Priority 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 for checkpoint 2.1

2.2 For a presentation that requires user input within a specified time interval controlled by the user agent, allow the user to configure the user agent to pause the presentation automatically and await user input before proceeding. [Priority 1]

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. In SMIL 1.0 [SMIL], for example, the "begin", "end", and "dur" attributes synchronize presentation components. This checkpoint does not apply when the user agent cannot recognize the time interval in the presentation format, or when the user agent cannot control the timing (e.g., because it is controlled by the server).

Techniques for checkpoint 2.2

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]

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 for checkpoint 2.3

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]

Content type labels: NoVideo, NoAudio.

Techniques for checkpoint 2.4

2.5 Respect author-specified synchronization cues during rendering. [Priority 1]

Content type labels: NoVideo, NoAudio.

Techniques for checkpoint 2.5

2.6 Allow configuration to generate repair text when the user agent recognizes that the author has failed to provide a required equivalent. If the content missing an equivalent is included by URI reference, base the repair text on the URI reference and content type. Otherwise, base the repair text on element type information. [Priority 2]

Note: 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. See also checkpoint 2.7.

Techniques for checkpoint 2.6

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]

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. See also checkpoint 2.6.

Techniques for checkpoint 2.7

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]

Note: For example, use a text substitute or accessible graphical icon to indicate that content in a particular language has not been rendered. This checkpoint does not require the user agent to allow different configurations for different natural languages.

Techniques for checkpoint 2.8

Ensure that the user may turn off rendering of content (audio, video, scripts, etc.) that may reduce accessibility by obscuring content or disorienting the user.

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 re-render the text every time it blinks. Distracting background images, colors, or sounds may 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 disabilities.

To ensure that users have access to content, user agents must allow them to configure the user agent not to render certain content types when loading a Web resource. A user agent must allow this configurability even when it passes 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.

This guideline requires the user agent to allow configuration so that, when loading a Web resource, the user agent does not render portions of that resource that are of a particular type, or the user agent will render those portions in a way that does not pose accessibility problems.

Requirements for interactive control of rendered content are part of guideline 4.

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]

Content type labels: NoImage.

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 for checkpoint 3.1

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 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]

Content type labels: NoAnimation, NoVideo, NoAudio.

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. See also checkpoint 4.5, checkpoint 4.9 and checkpoint 4.10.

Techniques for checkpoint 3.2

3.3 Allow the user to configure the user agent to render animated or blinking text as motionless, unblinking text. [Priority 1]

Content type labels: NoVisualText.

Note: This checkpoint does not apply for blinking and animation effects that are caused by mechanisms that the user agent cannot recognize.

Techniques for checkpoint 3.3

3.4 Allow the user to configure the user agent to render blinking images as motionless, unblinking images. [Priority 1]

Content type labels: NoAnimation.

Techniques for checkpoint 3.4

3.5 Allow the user to configure the user agent not to execute any scripts or applets. In this configuration, provide an option to alert the user when scripts or applets are available (but have not been executed). [Priority 1]

Techniques for checkpoint 3.5

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 on demand (e.g., by following a link or confirming a prompt). The user agent is not required to provide these functionalities for client-side redirects that occur instantaneously (i.e., when there is no delay before the new content is retrieved). [Priority 2]

Techniques for checkpoint 3.6

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 on demand (e.g., by following a link or confirming a prompt). 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]

Techniques for checkpoint 3.7

3.8 Allow the user to configure the user agent not to render images. In this configuration, provide an option to render a placeholder in context for each unrendered image. When placeholders are rendered, allow the user to activate each placeholder individually and replace it with the original author-supplied content. [Priority 2]

Content type labels: NoImage.

Techniques for checkpoint 3.8

Ensure that the user can select preferred styles (colors, size of rendered text, synthesized speech characteristics, etc.) from choices offered by the user agent. The user must be able to override author-specified styles and user agent default styles.

Providing access to content (see guideline 2) includes enabling users to configure its rendering. Users with low vision may require that text be rendered at a size larger than the size specified by the author or the user agent's default. Users with color blindness may need to impose or prevent certain color combinations.

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-only 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 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. Users need to be alerted to changes to content or viewports that the users did not initiate (e.g., when a viewport opens automatically).

Note: The checkpoints in this guideline apply to all content, including equivalents.

Checkpoints for visually rendered text (content accessibility):

4.1 Allow the user to configure globally and control the reference size of rendered text, with an option to override reference sizes specified by the author or user agent defaults. Allow the user to choose from among the full range of font sizes supported by the system. [Priority 1]

Content type labels: NoVisualText.

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 for checkpoint 4.1

4.2 Allow the user to configure globally the font family of all rendered text, with an option to override font families specified by the author or user agent defaults. Allow the user to choose from among the full range of font families supported by the system. [Priority 1]

Content type labels: NoVisualText.

Note: For example, allow the user to specify that all text must be rendered in a particular sans-serif font family. For text that cannot be rendered properly using the user's selected font family, the user agent may select an alternative font family.

Techniques for checkpoint 4.2

4.3 Allow the user to configure globally the foreground and background color of all rendered text, with an option to override foreground and background colors specified by the author or user agent defaults. Allow the user to choose from among the full range of colors supported by the system. [Priority 1]

Content type labels: NoColorText.

Note: User configuration of foreground and background colors may result in the inability to distinguish ordinary text from selected text, focused text, etc. See checkpoint 8.2 for more information about highlight styles.

Techniques for checkpoint 4.3

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. For a visual track, provide at least one setting between 40% and 60% of the original speed. For a prerecorded audio track including audio-only presentations, provide at least one setting between 75% and 80% of the original speed. When the user agent allows the user to slow the visual track of a synchronized multimedia presentation to between 100% and 80% of its original speed, synchronize the visual and audio tracks. Below 80%, the user agent is not required to render the audio track. The user agent is not required to satisfy this checkpoint for audio, video and animations whose recognized role is to create a purely stylistic effect. [Priority 1]

Content type labels: NoAnimation, NoVideo, NoAudio.

Note: Purely stylistic effects include background sounds, decorative animated images, and effects caused by style sheets. The style exception of this checkpoint is based on the assumption that authors have satisfied the requirements of the "Web Content Accessibility Guidelines 1.0" [WCAG10] not to convey information through style alone (e.g., through color alone or style sheets alone). See also checkpoint 4.7.

See also checkpoint 2.5.

Techniques for checkpoint 4.4

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. The user agent is not required to satisfy this checkpoint for audio, video and animations whose recognized role is to create a purely stylistic effect. [Priority 1]

Content type labels: NoAnimation, NoVideo, NoAudio.

Note: See checkpoint 4.4 for more information about the exception for purely stylistic effects. 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. See also checkpoint 3.2.

Techniques for checkpoint 4.5

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]

Techniques for checkpoint 4.6

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]

Content type labels: NoAnimation, NoVideo, NoAudio.

Note: User agents automatically satisfy this checkpoint if they satisfy checkpoint 4.4 for every audio, video, and animation.

Techniques for checkpoint 4.7

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]

Content type labels: NoAnimation, NoVideo, NoAudio.

Note: User agents automatically satisfy this checkpoint if they satisfy checkpoint 4.5 for every audio, video, and animation.

Techniques for checkpoint 4.8

Checkpoints for audio volume control (content accessibility):

4.9 Allow the user to configure globally and control the volume of all audio, with an option to override audio volumes specified by the author or user agent defaults. The user must be able to choose zero volume (i.e., silent). [Priority 1]

Content type labels: NoAudio.

Note: User agents should allow configuration and control of volume through available system-level controls.

Techniques for checkpoint 4.9

4.10 Allow the user to control independently the volumes of distinct audio sources synchronized to play simultaneously. [Priority 1]

Content type labels: NoAudio.

Note: Sounds that play at different times are distinguishable and therefore independent control of their volumes is not part of this checkpoint (volume control per checkpoint 4.9 suffices). The user agent may satisfy this checkpoint by allowing the user to control independently the volumes of all distinct audio sources. The user control required by this checkpoint includes the ability to override author-specified volumes for the relevant sources of audio. See also checkpoint 4.12.

Techniques for checkpoint 4.10

Checkpoints for synthesized speech (content accessibility):

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]

Content type labels: NoSpeech.

Note: The range of playback rates offered by the speech synthesizer may depend on the natural language.

Techniques for checkpoint 4.11

4.12 Allow the user to control synthesized speech volume independent of other sources of audio. [Priority 1]

Content type labels: NoSpeech.

Note: The user control required by this checkpoint includes the ability to override author-specified speech volume. See also checkpoint 4.10.

Techniques for checkpoint 4.12

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]

Content type labels: NoSpeech.

Note: Many speech synthesizers allow users to choose from among preset options that control different voice parameters (gender, pitch range, stress, richness, etc.) as a group. When using these synthesizers, allow the user to choose from among the full range of preset options (e.g., "adult male voice", "female child voice", "robot voice", etc.). 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 for checkpoint 4.13

Checkpoints for user interface accessibility:

4.14 For user agents that support style sheets, allow the user to choose from (and apply) available author and user style sheets or to ignore them. [Priority 1]

Note: By definition, the user agent's default style sheet is always present, but may be overridden by author or user styles.

Techniques for checkpoint 4.14

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]

Techniques for checkpoint 4.15

4.16 Ensure that when a viewport's selection or content focus changes, it is in the viewport after the change. [Priority 2]

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 for checkpoint 4.16

4.17 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 with which it overlaps. [Priority 2]

Techniques for checkpoint 4.17

4.18 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 on demand (e.g., by following a link or confirming a prompt). Allow the user to close viewports. If a viewport (e.g., a frame set) contains other viewports, these requirements only apply to the outermost container viewport. [Priority 2]

Note: User creation of a new viewport (e.g., empty or with a new resource loaded) through the user agent's user interface constitutes an explicit user request. See also checkpoint 4.15 (for control over changes of focus when a viewport opens) and checkpoint 5.5.

Techniques for checkpoint 4.18

4.19 Allow configuration so the user is prompted to confirm any viewport that closes without explicit user request. [Priority 3]

Techniques for checkpoint 4.19

Communicate with other software (e.g., assistive technologies, the operating system, plug-ins). Observe system and programming language conventions for the user agent user interface, documentation, installation, etc.

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 technologies.
• 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.
• 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).

Using interoperable APIs and following system conventions increases predictability for users and for developers of assistive technologies. 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 reimplement.

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]

Note: Please refer to the "Document Object Model (DOM) Level 2 Core Specification" [DOM2CORE] for information about HTML and XML versions covered.

Techniques for checkpoint 5.1

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]

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 for checkpoint 5.2

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.

Techniques for checkpoint 5.3

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]

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 for checkpoint 5.4

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]

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 the checkpoints of guideline 5.

Techniques for checkpoint 5.5

5.6 Implement standard accessibility APIs (e.g., 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]

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 for checkpoint 5.6

5.7 Implement the operating system's standard APIs for the keyboard. [Priority 1]

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. See also checkpoint 9.4.

Techniques for checkpoint 5.7

5.8 Ensure that programmatic exchanges proceed in a timely manner. [Priority 2]

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 for checkpoint 5.8

5.9 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 2]

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 for checkpoint 5.9

Checkpoints for user interface accessibility:

5.10 Follow operating system conventions that benefit accessibility when implementing the selection, content focus, and user interface focus. [Priority 1]

Note: This checkpoint is an important special case of checkpoint 5.12. See also checkpoint 7.1.

Techniques for checkpoint 5.10

5.11 Ensure that default input configurations do not interfere with operating system accessibility conventions. [Priority 1]

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]. See also checkpoint 9.4.

Techniques for checkpoint 5.11

5.12 Follow operating system conventions that benefit accessibility. In particular, follow conventions that benefit accessibility for user interface design, keyboard configuration, product installation, and documentation. [Priority 2]

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]. See also checkpoint 5.11.

Techniques for checkpoint 5.12

5.13 Follow operating system conventions to indicate the input configuration. [Priority 2]

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 5.12. See also checkpoint 9.4.

Techniques for checkpoint 5.13

Support the accessibility features of all implemented specifications. Implement W3C Recommendations when available and appropriate for a task.

Developers should implement open specifications. Conformance to open specifications benefits 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 recommends conformance to W3C specifications for several reasons:

• W3C specifications include "built-in" accessibility features.
• W3C specifications undergo early review to ensure that accessibility issues are considered during the design phase. This review includes review from stakeholders in accessibility.
• W3C specifications are developed in a consensus process (refer to the process defined by the W3C Process Document [W3CPROCESS]). W3C encourages the public to review and comment on these specifications (public Working Drafts, Candidate Recommendations, and Proposed Recommendations). 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 site.

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]

Note: This checkpoint applies to both W3C-developed and non-W3C specifications. The Techniques document [UAAG10-TECHS] provides information about the accessibility features of some specifications, including W3C specifications.

Techniques for checkpoint 6.1

6.2 Use and conform to W3C Recommendations when they are available and appropriate for a task. [Priority 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, see 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 for checkpoint 6.2

Provide access to content through a variety of navigation mechanisms: sequential navigation, direct navigation, searches, structured navigation, etc.

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 it is an active element), and recall the surrounding context (to orient themselves). Providing a variety of navigation mechanisms helps users with disabilities (and all users) access content more efficiently. Content navigation is particularly important to users who access content serially (e.g., as synthesized speech or braille).

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 also benefits 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), to users with visual disabilities, and also benefits "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 offer both context and speed. User agents should allow users to navigate to content known to be structurally important: blocks of content, headers and sections, tables, forms and form elements, active elements, navigation mechanisms, containers, etc. For information about programmatic access to document structure, see 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.).

Checkpoints for user interface accessibility:

7.1 Allow the user to navigate among all viewports (including frames). [Priority 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 for checkpoint 7.1

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]

Note: For example, when the user navigates from one viewport to another (per checkpoint 7.1) and back, restore the point of regard.

Techniques for checkpoint 7.2

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]

Note: The set of navigable elements required by this checkpoint must include active elements and may include non-active elements. This checkpoint is an important special case of checkpoint 7.6.

Techniques for checkpoint 7.3

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]

Note: The set of navigable elements required by this checkpoint must include active elements and must not include non-active elements.

Techniques for checkpoint 7.4

7.5 Allow the user to search within rendered text content for a sequence of characters from the document character set. Allow the user to start a forward search (in document order) from any selected or focused location in content. When there is a match (1) move the viewport so that the matched text content is within it, and (2) allow the user to search for the next instance of the text from the location of the match. Alert the user when there is no match. If the search wraps back to the beginning of content, alert the user prior to wrapping. Provide a case-insensitive search option for text in scripts (i.e., writing systems) where case is significant. [Priority 2]

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). A wrapping search is one that restarts automatically at the beginning of content once the end of content has been reached.

Techniques for checkpoint 7.5

7.6 Allow the user to navigate efficiently to and among important structural elements. Allow forward and backward sequential navigation to important structural elements. [Priority 2]

Note: This specification intentionally does not identify which "important elements" must be navigable as this will vary according to markup language. What constitutes "efficient navigation" may depend on a number of factors as well, including the "shape" of content (e.g., serial navigation of long lists is not efficient) and desired granularity (e.g., among tables, then among the cells of a given table). Refer to the Techniques document [UAAG10-TECHS] for information about identifying and navigating important elements. See also checkpoint 7.7.

Techniques for checkpoint 7.6

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]

Note: For example, allow the user to navigate only paragraphs, or only headings and paragraphs, etc. See also checkpoint 5.4.

Techniques for checkpoint 7.7

Provide information that will help the user understand browsing context.

All users require clues to help them understand their "location" when browsing: where they are, how they got there, where they can go, what's nearby, etc. Some mechanisms that provide such clues include:

• information about browsing context such as proportional scroll bars, a visually highlighted selection, a history mechanism, the title of the current document or frame, etc. These clues must be available in a device-independent manner;
• information about elements, such as the dimensions of a table, the length of an audio clip, the structure of a form, whether following a link will involve a fee, etc.
• information about relationships among elements, such as between table cells and related table headers.

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.

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]

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. See also checkpoint 5.3. This checkpoint is an important special case of checkpoint 2.1.

Techniques for checkpoint 8.1