User Agent Accessibility Guidelines 2.0

Editor's Draft 10 January 2008

This version:

http://www.w3.org/WAI/UA/2008/WD-UAAG20-20080110/WD-UAAG20-20080110.html

Latest version:

N/A

Previous version:

http://www.w3.org/WAI/UA/2007/WD-UAAG20-20071107/WD-UAAG20-20071107.html

Editors:

James Allan, Texas School for the Blind and Visually Impaired

Jan Richards, Adaptive Technology Resource Centre, University of Toronto

Previous Editors:

NA

Copyright ©2007 W3C^® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Ensure that the user can interact with the user agent (and the content it renders) through different input and output devices.

Since people use a variety of devices for input and output, user agent developers need to ensure redundancy in the user interface. The user may have to operate the user interface with a variety of input devices (e.g., keyboard, pointing device, and voice input) and output modalities (e.g., graphical, speech, or braille rendering).

Enabling full user agent operation through the keyboard is an important part of promoting device-independence in target user agents. In addition to the fact that most operating environments include support for some form of keyboard, the reasons for this include:

• For some users (e.g., users with blindness or physical disabilities), operating a user agent with a pointing device may be difficult or impossible since it requires tracking the pointing device position in a two-dimensional visual space. Keyboard operation generally makes fewer perceptual/motor demands for moving the pointing device to a visual target.
• Some assistive technologies that support a diversity of input and output mechanisms use keyboard APIs for communication with some user agents; see checkpoint 6.7. People who cannot or do not use a pointing device may interact with the user interface with the keyboard, through voice input, a head wand, touch screen, or other device.

While this document only requires keyboard operation for conformance, it promotes input device independence by also allowing people to claim conformance for full pointing device support or full voice support.

As a way to promote output device independence, this guideline requires support for text messages in the user interface because text may be rendered visually, as synthesized speech, or as braille.

The API requirements of guideline 6 also promote device independence by ensuring communication with other software, including assistive technologies.

Checkpoint definitions

1.1 Full keyboard access (P1) Techniques for checkpoint 1.1

@@7.2, 7.4 Possibly move here@@

@@CL: "Precedence of 'operations' - keys"

Note: For example, ensure that the user can interact with enabled elements, select content, navigate viewports, configure the user agent, access documentation, install the user agent, and operate user interface controls, all entirely through keyboard input.

User agents generally support at least three types of keyboard operation:

1. Direct (e.g., keyboard shortcuts such as "F1" to open the help menu; see checkpoint 11.4 for single-key access requirements),
2. Sequential (e.g., navigation through cascading menus), and
3. Spatial (e.g., when the keyboard is used to move the pointing device in two-dimensional visual space to manipulate a bitmap image).

User agents should support direct or sequential keyboard operation for all functionalities. Furthermore, the user agent should satisfy this checkpoint by offering a combination of keyboard-operable user interface controls (e.g., keyboard operable print menus and settings) and direct keyboard shortcuts (e.g., to print the current page).

It is also possible to claim conformance to this document for full support through pointing device input and/or voice input. See the section on Input modality labels.

1.2 Manage event handlers (P1) Techniques for checkpoint 1.2

Note: Refer to the checkpoints of guideline 9 for more information about focus requirements.

1.3 Text alternatives for non-text objects (P1) Techniques for checkpoint 1.3

Note: For example, if the user is alerted of an event by an audio cue, a visually-rendered text equivalent in the status bar could satisfy this checkpoint. Per checkpoint 6.5, a text equivalent for each such message must be available through an API. See also checkpoint 6.6 for requirements for programmatic notification of changes to the user interface. Examples of priority properties for a text message are off (not currently live), polite (low priority), assertive (medium priority), and rude (high priority) for AJAX live regions.

Ensure that users have access to all content, notably conditional content that may have been provided to meet the requirements of the Web Content Accessibility Guidelines 2.0 [WCAG20].

The checkpoints in this section require the user agent to provide access to all content through a series of complementary mechanisms designed so that if one fails, another will provide some access. The following preferences are embodied in the checkpoints:

• Both manual and automatic selection of which conditional content to render are important to accessibility.
• Both structured navigation and unstructured access to content are important to accessibility.
• Rendering according to format specification is preferred, but a source view of text content may be necessary for access (e.g., because of user-side error conditions, authoring errors, inadequate specification, or incorrect user agent implementation). For example, in order to find necessary information, the user may have to look at Uniform Resource Identifiers (URIs) for information, HTML comments, XML element names, or script data.
• Configuration and control of rendering are important for access. For instance, the user agent should respect authoring synchronization cues for content that changes over time, but also needs to allow the user to control the time intervals when user input might otherwise be impossible.

Authors may use the conditional content mechanisms of a specification to satisfy the requirements of the Web Content Accessibility Guidelines 2.0 [WCAG20]. Ensuring access to conditional content 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 a configuration preference (e.g., they have a slow Internet connection and prefer not to download movies or images).

Checkpoint definitions

2.1 Render content according to specification (P1) Techniques for checkpoint 2.1

1. Render content according to format specification (e.g., for a markup language or style sheet language).

Note: If a conforming user agent does not render a content type, it should allow the user to choose a way to handle that content (e.g., by launching another application or by saving it to disk).

2.2 Provide text view (P1) Techniques for checkpoint 2.2

1. For content authored in text formats, provide a view of the text source.

2.3 Render conditional content (P1) Techniques for checkpoint 2.3

Note: For instance, an HTML user agent might allow users to query each element for access to conditional content supplied for the alt, title, and longdesc attributes. Or, the user agent might allow configuration so that the value of the alt attribute is rendered in place of all IMG elements (while other conditional content might be made available through another mechanism). User agents should expose configuration choices in as highly visible a fashion as is practical such as on a menu entry or dialog settings devoted to accessibility.

2.4 Allow time-independent interaction (P1) Techniques for checkpoint 2.4

1. For rendered content where user input is only possible within a finite time interval controlled by the user agent, allow configuration to provide a view where user interaction is time-independent.

Note: If the user agent satisfies this checkpoint by pausing automatically, it may be necessary to pause more than once when there are multiple opportunities for time-sensitive user interaction. When pausing, pause synchronized content as well (whether rendered in the same or different viewports) per checkpoint 2.6. In SMIL 1.0 [SMIL], for example, the begin, end, and dur attributes synchronize presentation components. See also checkpoint 3.4, which involves client-driven content retrieval.

2.5 Make captions, transcripts, audio descriptions available (P1) Techniques for checkpoint 2.5

1. Allow configuration or control to render text transcripts, collated text transcripts, captions, and audio descriptions in content at the same time as the associated audio tracks and visual tracks.

2.6 Respect synchronization cues (P1) Techniques for checkpoint 2.6

1. Respect synchronization cues (e.g., in markup) during rendering.

2.7 Repair missing content (P2) Techniques for checkpoint 2.7

1. Allow configuration to generate repair text when the user agent recognizes that the author has not provided conditional content required by the format specification.

Note: Some markup languages (such as HTML 4 [HTML4] and SMIL 1.0 [SMIL] require the author to provide conditional content for some elements (e.g., the alt attribute on the IMG element).

2.8 No repair text (P3) Techniques for checkpoint 2.8

1. Allow at least two configurations for when the user agent recognizes that conditional content required by the format specification is present but empty content:
   • generate no repair text.
   • generate repair as described in checkpoint 2.7.

Note: In some authoring scenarios, empty content (e.g., alt="" in HTML) may make an appropriate text equivalent, such as when non-text content has no other function than pure decoration, or when an image is part of a "mosaic" of several images and does not make sense out of the mosaic. Refer to the Web Content Accessibility Guidelines 2.0 [WCAG20] for more information about text equivalents.

2.9 Render conditional content automatically (P3) Techniques for checkpoint 2.9

1. Allow configuration to render all conditional content automatically.
2. As part of satisfying provision one of this checkpoint, provide access according to specification, or where unspecified, by applying one of the techniques 1a, 2a, or 1b defined in provision two of checkpoint 2.3.

Note: For instance, an HTML user agent might allow configuration so that the value of the alt attribute is rendered in place of all IMG elements (while other conditional content might be made available through another mechanism).

2.10 Don't render text in unsupported writing systems (P3) Techniques for checkpoint 2.10

1. For graphical user agents, allow configuration not to render text in unsupported scripts (i.e., writing systems) when that text would otherwise be rendered.
2. When configured per provision one of this checkpoint, indicate to the user in context that author-supplied content has not been rendered due to lack of support for a writing system.

Note: The primary purpose of this checkpoint is to benefit users with serial access to content or who navigate sequentially, allowing them to skip portions of content that would be unusable if rendered graphically as "garbage."

Ensure that the user may turn off rendering of content (e.g., audio, video, scripts) that may reduce accessibility by obscuring other 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 text can affect screen reader users, since screen readers (in conjunction with speech synthesizers or braille displays) may re-render the text every time it blinks. 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 (e.g., viewports that open without notice or automatic content retrieval) may disorient some users with cognitive disabilities.

This guideline requires the user agent to allow configuration so that, when loading Web resources, the user agent does not render content in a manner that might pose accessibility problems. Requirements for interactive control of rendered content are part of guideline 4.

Checkpoint definitions

3.1 Toggle background images (P1) Techniques for checkpoint 3.1

1. Allow configuration not to render images that are rendered on the base background.

Note: When background images are not rendered, they are considered conditional content. See checkpoint 2.3 for information about providing access to conditional content.

3.2 Toggle audio, video, animated images, and animated/blinking text (P1) Techniques for checkpoint 3.2

1. Allow configuration not to render audio, video, or animated image content, except on explicit user request.
2. Allow configuration to render animated or blinking text content as motionless, unblinking text.

Note: See guideline 4 for additional requirements related to the control of rendered audio, video, and animated images. When these content types are not rendered, they are considered conditional content. See checkpoint 2.3 for information about providing access to conditional content. Animation (a rendering effect) differs from streaming (a delivery mechanism). Streaming content might be rendered as an animation (e.g., an animated stock ticker or vertically scrolling text) or as static text (e.g., movie subtitles, which are rendered for a limited time, but do not give the impression of movement).

3.3 Toggle executable content (P1) Techniques for checkpoint 3.3

1. Allow configuration not to execute any executable content (e.g., scripts, objects and applets).

Note: Executable content may provide very useful functionality, not all of which causes accessibility problems. If content is not executed it is important to instead render any conditional content that the author may provide.@@take another look at this@@

3.4 Toggle automatic content retrieval (P1) Techniques for checkpoint 3.4

1. Allow configuration so that the user agent only retrieves content on explicit user request.

Note: For example, if the user agent supports automatic content retrieval, to ensure that the user does not become disoriented by sudden automatic changes, allow configurations such as "Never retrieve content automatically" and "Require confirmation before content retrieval."

3.5 Toggle images (P2) Techniques for checkpoint 3.5

1. Allow configuration not to render image content.

Note: When images are not rendered, they are considered conditional content. See checkpoint 2.3 for information about providing access to conditional content.

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

Providing access to content (see guideline 2) includes enabling users to configure and control its rendering. Users with low vision may require that text be rendered at a size larger than the size specified by the author or by the user agent's default rendering. 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 frame assumed by the author. To make the presentation accessible to these users, user agents rendering multimedia content (audio, video, and other animations), have to allow the user to control the playback rate of this content, and also to stop, start, pause, and navigate it quickly. User agents rendering audio have to allow the user to control the audio volume globally and to allow the user to control distinguishable audio tracks.

User agents with speech synthesis capabilities need to allow users to control various synthesized speech rendering parameters. For instance, some users may not be able to make use of high or low frequencies; these users have to be able to configure their speech synthesizers to use suitable frequencies.

Checkpoint definitions for visually rendered text

4.1 Configure text scale (P1) Techniques for checkpoint 4.1

1. Allow global configuration of the scale of visually rendered text content. Preserve distinctions in the size of rendered text as the user increases or decreases the scale.
2. As part of satisfying provision one of this checkpoint, provide a configuration option to override rendered text sizes specified by the author or user agent defaults.
3. As part of satisfying provision one of this checkpoint, offer a range of text sizes to the user that includes at least:
   • the range offered by the conventional utility available in the operating environment that allows users to choose the text size (e.g., the font size), or
   • if no such utility is available, the range of text sizes supported by the conventional APIs of the operating environment for drawing text.

4.2 Configure font family (P1) Techniques for checkpoint 4.2

1. Allow global configuration of the font family of all visually rendered text content.
2. As part of satisfying provision one of this checkpoint, provide a configuration option to override font families specified by the author or by user agent defaults.
3. As part of satisfying provision one of this checkpoint, offer a range of font families to the user that includes at least:
   • the range offered by the conventional utility available in the operating environment that allows users to choose the font family, or
   • if no such utility is available, the range of font families supported by the conventional APIs of the operating environment for drawing text.

Note: For example, allow the user to specify that all text is to be rendered in a particular sans-serif font family.

4.3 Configure text colors (P1) Techniques for checkpoint 4.3

1. Allow global configuration of the foreground and background color of all visually rendered text content.
2. As part of satisfying provision one of this checkpoint, provide a configuration option to override foreground and background colors specified by the author or user agent defaults.
3. As part of satisfying provision one of this checkpoint, offer a range of colors to the user that includes at least:
   • the range offered by the conventional utility available in the operating environment that allows users to choose colors, or
   • if no such utility is available, the range of colors supported by the conventional APIs of the operating environment for specifying colors.

Note: User configuration of foreground and background colors may inadvertently lead to the inability to distinguish ordinary text from selected text or focused text. See checkpoint 10.2 for more information about highlight styles.

Checkpoint definitions for multimedia presentations and other presentations that change continuously over time

4.4 Slow multimedia (P1) Techniques for checkpoint 4.4

1. Allow the user to slow the presentation rate of rendered audio and animation content (including video and animated images).
2. As part of satisfying provision one of this checkpoint, for a visual track, provide at least one setting between 40% and 60% of the original speed.
3. As part of satisfying provision one of this checkpoint, for a prerecorded audio track including audio-only presentations, provide at least one setting between 75% and 80% of the original speed.
4. 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 (per checkpoint 2.6). Below 80%, the user agent is not required to render the audio track.

Note: The style exception of this checkpoint is based on the assumption that authors have satisfied the requirements of the "Web Content Accessibility Guidelines 2.0" [WCAG20] not to convey information through style alone (e.g., through color alone or style sheets alone). @@RE-LOOK AT THIS NOTE@@

4.5 Start, stop, pause, and navigate multimedia (P1) Techniques for checkpoint 4.5

1. Allow the user to stop, pause, and resume rendered audio and animation content (including video and animated images) that last three or more seconds at their default playback rate.
2. Allow the user to navigate efficiently within rendered audio and animations (including video and animated images) that last three or more seconds at their default playback rate.

Note: The lower bound of three seconds is part of this checkpoint since control is not required for brief audio and animation content, such as short clips or beeps. Respect synchronization cues per checkpoint 2.6.

4.6 Do not obscure captions (P1) Techniques for checkpoint 4.6

1. For graphical viewports, allow configuration so that captions synchronized with a visual track in content are not obscured by it.

Checkpoint definitions for audio volume control

4.7 Global volume control (P1) Techniques for checkpoint 4.7

1. Allow global configuration of the volume of all rendered audio.
2. As part of satisfying provision one of this checkpoint, allow the user to choose zero volume (i.e., silent).

Note: User agents should allow configuration of volume through available operating environment mechanisms.

4.8 Independent volume control (P1) Techniques for checkpoint 4.8

1. Allow independent control of the volumes of rendered audio content synchronized to play simultaneously.

Note: The user agent should satisfy this checkpoint by allowing the user to control independently the volumes of all audio sources (e.g., by implementing a general audio mixer type of functionality). See checkpoint 4.10 for information about controlling the volume of synthesized speech.

Checkpoint definitions for synthesized speech rendering

4.9 Configure synthesized speech rate (P1) Techniques for checkpoint 4.9

1. Allow configuration of the synthesized speech rate, according to the full range offered by the speech synthesizer.

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

4.10 Configure synthesized speech volume (P1) Techniques for checkpoint 4.10

1. Allow control of the synthesized speech volume, independent of other sources of audio.

Note: See checkpoint 4.8 for information about independent volume control of different sources of audio.

4.11 Configure synthesized speech characteristics (P1) Techniques for checkpoint 4.11

1. Allow configuration of synthesized speech characteristics according to the full range of values offered by the speech synthesizer.

Note: Some speech synthesizers allow users to choose values for synthesized speech characteristics at a higher abstraction layer, i.e., by choosing from present options that group several characteristics. Some typical options one might encounter include: voice (e.g., adult male voice, female child voice, robot voice), pitch, and stress. Ranges for values may vary among speech synthesizers.

4.12 Specific synthesized speech characteristics (P2) Techniques for checkpoint 4.12

1. Allow configuration of synthesized speech pitch. Pitch refers to the average frequency of the speaking voice.
2. Allow configuration of synthesized speech pitch range. Pitch range specifies a variation in average frequency.
3. Allow configuration of synthesized speech stress. Stress refers to the height of "local peaks" in the intonation contour of the voice.
4. Allow configuration of synthesized speech richness. Richness refers to the richness or brightness of the voice.

Note: This checkpoint is more specific than checkpoint 4.11. It requires support for the voice characteristics listed in the provisions of this checkpoint. Definitions for these characteristics are based on descriptions in section 19 of the Cascading Style Sheets Level 2 Recommendation [CSS2]; refer to that specification for additional informative descriptions. Some speech synthesizers allow users to choose values for synthesized speech characteristics at a higher abstraction layer, for example, by choosing from present options distinguished by gender, age, or accent. Ranges of values may vary among speech synthesizers.

4.13 Configure synthesized speech features (P2) Techniques for checkpoint 4.13

1. Provide support for user-defined extensions to the synthesized speech dictionary.
2. Provide support for spell-out: where text is spelled one character at a time, or according to language-dependent pronunciation rules.
3. Allow at least two configurations for speaking numerals: one where numerals are spoken as individual digits, and one where full numbers are spoken.
4. Allow at least two configurations for speaking punctuation: one where punctuation is spoken literally, and one where punctuation is rendered as natural pauses.

Note: Definitions for the functionalities listed in the provisions of this checkpoint are based on descriptions in section 19 of the Cascading Style Sheets Level 2 Recommendation [CSS2]; refer to that specification for additional informative descriptions.

Checkpoint definitions related to style sheets

4.14 Choose style sheets (P1) Techniques for checkpoint 4.14

1. Allow the user to choose from and apply alternative author style sheets (such as linked style sheets).
2. Allow the user to choose from and apply at least one user style sheet.
3. Allow the user to turn off (i.e., ignore) author and user style sheets.

Note: By definition, the user agent's default style sheet is always present, but may be overridden by author or user styles. Developers should not consider that the user's ability to turn off author and user style sheets is an effective way to improve content accessibility; turning off style sheet support means losing the many benefits they offer. Instead, developers should provide users with finer control over user agent or content behavior known to raise accessibility barriers. The user should only have to turn off author and user style sheets as a last resort.

Ensure that the user can control the behavior of viewports and user interface controls, including those that may be manipulated by the author (e.g., through scripts).

Control of viewport behavior is important to accessibility. Unexpected changes to the point of regard — what the user is presumed to be viewing — may cause users to lose track of how many viewports are open, or which viewport has the current focus. If carried out automatically, these changes might go unnoticed (e.g., by some users with blindness) or be disorienting (e.g., to some users with a cognitive disability). This guideline includes requirements for control of opening and closing viewports, the relative position of graphical viewports, changes to focus, and inadvertent form submissions.

Checkpoint definitions

Guideline: 5.X Manage viewport opening

5.1 No automatic content focus change (P2) Techniques for checkpoint 5.1

1. Allow configuration so that if a viewport opens without explicit user request, neither its content focus nor its user interface focus automatically becomes the current focus.

5.2 Keep viewport on top (P2) Techniques for checkpoint 5.2

1. For graphical user interfaces, allow configuration so that the viewport with the current focus remains "on top" of all other viewports with which it overlaps.

5.3 Manual viewport open only (P2) Techniques for checkpoint 5.3

1. Allow configuration so that viewports only open on explicit user request.
2. When configured per provision one of this checkpoint, instead of opening a viewport automatically, alert the user and allow the user to open it with an explicit request (e.g., by confirming a prompt or following a link generated by the user agent).
3. Allow the user to close viewports.

Note: Generally, viewports open automatically as the result of instructions in content. See also checkpoint 5.1 (for control over changes of focus when a viewport opens) and checkpoint 6.6 (for programmatic notification of changes to the user interface).