User Agent Accessibility Guidelines 1.0

12 September 2001

2. The user agent accessibility guidelines

The twelve 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 visually rendered text" and second group of "checkpoints for audio volume control"." Within each group, checkpoints are ordered according to their priority, e.g., Priority 1 before Priority 2. Within a guideline, checkpoint groupings and checkpoint order have no bearing on conformance.

Each checkpoint definition includes the following parts. Some parts are normative (i.e., relate to conformance); others are informative only.

• The checkpoint number.
• The checkpoint title. This title is not a requirement, just a phrase to help readers remember an important requirement made by the checkpoint statement. (Informative)
• The priority of the checkpoint. (Normative)
• The statement or statements of the checkpoint. These statements include one or more requirements that must be satisfied by the user agent (i.e., the "subject of the claim) for the purposes of conformance. (Normative)
• An optional "content/rendered content/user agent feature/both" label that indicates whether the requirements of the checkpoint must be satisfied by the subject of the claim for all content, all rendered content, for user agent features only, or for both content and user agent features. The label only appears when necessary to disambiguate the checkpoint. (Normative)
• A link to rationale, implementation details, references, and more information in "Techniques for User Agent Accessibility Guidelines 1.0" [UAAG10-TECHS]. (Informative)
• Content type labels (zero or more). Content type labels are explained in the section on conformance. (Normative)
• Optional notes about the checkpoint (beginning with the word "Note"). They notes clarify the scope of the checkpoint through further description, examples, cross references, and commentary. Some checkpoints in this document are more general than others, and some may overlap in scope. Therefore, a checkpoint may be identified as a "special case" or an "important special case" of one or more other checkpoints. (Informative)

Each checkpoint definition expresses one or more requirements. These requirements are not technology specific. In fact, they have been designed to be largely technology independent, in order to make sense for a variety of existing and future technologies. "Techniques for User Agent Accessibility Guidelines 1.0" [UAAG10-TECHS] is an important resource to help developers understand how to "apply" the requirements to HTML, CSS, SMIL, and SVG, and several operating environments. The User Agent Accessibility Guidelines Working Group welcomes comments and anticipates discussion on how to apply these requirements to new technologies in different operating environments.

Each requirement is a "minimal" requirement, which means that for conformance, the user agent is required to satisfy no more than the stated requirement. In many cases, however, it may be easier or less costly (or just be better design) to implement a general feature that satisfies more than a minimal requirement. One general solution might satisfy five checkpoints and be easier to implement than five disconnected features. For instance, a navigable structure view of content that allows users to query elements for their properties is likely to benefit all users and may be used to satisfy a number of requirements of this document.

Some requirements have a wider impact than others. For instance, the keyboard requirements of checkpoint 1.1 have an impact on all other requirements in the document related to user input: any requirement that involves user input must be satisfied through the keyboard. Because the keyboard requirements of checkpoint 1.1 have been factored out, the other checkpoints are shorter; they are written "Allow configuration" instead of "Allow configuration through the keyboard." First-time readers of the document are encouraged to read the full context provided for each checkpoint, including the guideline prose, the surrounding checkpoints (since nearby checkpoints are generally related), notes after checkpoints, and associated techniques (in the Techniques document [UAAG10-TECHS]). The checklist [UAAG10-CHECKLIST] is also a useful tool (e.g., for evaluating a user agent for conformance), but does not provide the same contextual support.

Priorities

Each checkpoint in this document is assigned a priority that indicates its importance for users with disabilities.

Priority 1 (P1)

This checkpoint must be satisfied by user agents, otherwise one or more groups of users with disabilities will find it impossible to access the Web. Satisfying this checkpoint is a basic requirement for enabling some people to access the Web.

Priority 2 (P2)

This checkpoint should be satisfied by user agents, otherwise one or more groups of users with disabilities will find it difficult to access the Web. Satisfying this checkpoint will remove significant barriers to Web access for some people.

Priority 3 (P3)

This checkpoint may be satisfied by user agents to make it easier for one or more groups of users with disabilities to access information. Satisfying this checkpoint will improve access to the Web for some people.

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 (keyboard, pointing device, voice input, etc.) and output modalities (e.g., graphical, speech, or braille rendering).

Though it may seem contradictory, enabling full user agent operation through the keyboard is an important part of promoting device-independence given today's user agents. In addition to the fact that some form of keyboard is supported by most platforms, there are several reasons for this:

• 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 does not generally require as much movement "through space".
• Some assistive technologies that support a diversity of input and output mechanisms use keyboard APIs for communication with some user agents; see checkpoint 6.6. 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 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, and as braille.

The API requirements of guideline 6 also promote device independence by ensuring communication with specialized software.

Checkpoints

1.1 Full keyboard access. (P1)

1. Ensure that the user can operate through keyboard input alone any user agent functionality available through the user interface.

For both content and user agent. Techniques for checkpoint 1.1

Note: User agents may support at least two types of keyboard access to functionalities: direct access (where user awareness of a location "in space" is not required, as is the case with keyboard shortcuts and navigation of user agent menus) and spatial access (where the user moves the pointing device "in space" via the keyboard). To satisfy this checkpoint, user agents are expected to provide a mix of both types of keyboard access. User agents should allow direct keyboard access where possible, and this may be redundant with spatial input techniques. Furthermore, the user agent should satisfy this requirement by offering a combination of keyboard-operable user interface controls (e.g., keyboard operable print menus and settings) and direct keyboard operation of user agent functionalities (e.g., a short cut to print the current page). As examples of functionalities, ensure that the user can interact with enabled elements, select content, navigate viewports, configure the user agent, access documentation, install the user agent, operate controls of the user interface, etc., all entirely through keyboard input. It is also possible to claim conformance to this document for full support through pointing device input and voice input. See the section on input modality labels.

1.2 Activate event handlers. (P1)

1. For the element with content focus, allow the user to activate any explicitly associated input device event handlers through keyboard input alone.
2. The user agent is not required to allow activation of event handlers associated with a given device (e.g., the pointing device) in any order other than what the device itself allows.

Techniques for checkpoint 1.2

Note: The requirements for this checkpoint refer to any explicitly associated input device event handlers associated with an element, independent of the input modalities for which the user agent conforms. For example, suppose that an element has an explicitly associated handler for pointing device events. Even when the user agent only conforms for keyboard input (and does not conform for the pointing device, for example), this checkpoint requires the user agent to allow the user to activate that handler with the keyboard. This checkpoint is an important special case of checkpoint 1.1. Please refer to the checkpoints of guideline 9 for more information about focus requirements.

1.3 Provide text messages. (P1)

1. 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.

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 6.4, a text equivalent for each such message must be available through an API. See also checkpoint 6.5 for requirements for programmatic alert of changes to the user interface.

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 1.0 [WCAG10].

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:

• Not all content is rendered at all times. Automatic decision by the user agent about when and where to render conditional content is preferred, but manual choice by the user may be necessary for access.
• Structure is preferred (both the author's specified preferences and the user's structured access), but unstructured access may be necessary for access to all content.
• 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, the user may have to look at URIs for information, HTML comments, XML element names, or script data. 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 is possible.
• Configuration and control of rendering are important for access.

Authors may use the conditional content mechanisms of a specification to satisfy the requirements of the Web Content Accessibility Guidelines 1.0 [WCAG10]. 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 simply a configuration preference (e.g., they have a slow Internet connection and prefer not to download movies or images).

Checkpoints

2.1 Render content according to specification. (P1)

1. Render content according to format specification (e.g., for a markup language or style sheet).
2. When a rendering requirement of another specification contradicts a requirement of the current document, the user agent may disregard the rendering requirement of the other specification and still satisfy this checkpoint.
3. Rendering requirements include format-defined interactions between author preferences and user preferences/capabilities (e.g., when to render the "alt" attribute in HTML, the rendering order of nested OBJECT elements in HTML, test attributes in SMIL, and the cascade in CSS2).

Techniques for checkpoint 2.1

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, by saving it to disk, etc.). The user agent is not required to satisfy this checkpoint for all implemented specifications; see the section on conformance and implementing specifications for more information.

2.2 Provide text view. (P1)

1. For content authored in text formats, provide a view of the text source. For the purposes of this document, text formats are defined to be:
   • all media objects given an Internet media type of "text" (e.g., text/plain, text/HTML, or text/*) as defined in RFC 2046 [RFC2046], section 4.1.
   • all SGML and XML applications, regardless of Internet media type (e.g., HTML 4.01, XHTML 1.1, SMIL, SVG, etc.).

Techniques for checkpoint 2.2

Note: A user agent would also satisfy this checkpoint by providing a source view for any text format, not just implemented text formats. The user agent is not required to satisfy this checkpoint for all implemented specifications; see the section on conformance and implementing specifications for more information.

2.3 Render conditional content. (P1)

1. Allow configuration to provide access to each piece of unrendered conditional content "C".
2. The configuration may be a switch that, for all content, turns on or off the access mechanisms described in the next provision.
3. When a specification does not explain how to provide access to this content, do so as follows:
   • If C is a summary, title, alternative, description, or expansion of another piece of content D, provide access through at least one of the following mechanisms:
     • (1a) render C in place of D;
     • (2a) render C in addition to D;
     • (3a) provide access to C by querying D. In this case, the user agent must also alert the user, on a per-element basis, to the existence of C (so that the user knows to query D);
     • (4a) allow the user to follow a link to C from the context of D.
   • Otherwise, provide access to C through at least one of the following mechanisms:
     • (1b) render a placeholder for C, and allow the user to view the original author-supplied content associated with each placeholder;
     • (2b) provide access to C by query (e.g., allow the user to query an element for its attributes). In this case, the user agent must also alert the user, on a per-element basis, to the existence of C;
     • (3b) allow the user to follow a link in context to C.
4. To satisfy this checkpoint, the user agent may provide access on a per-element basis (e.g., by allowing the user to query individual elements) or for all elements (e.g., by offering a configuration to render conditional content all the time).

For all content. 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). See checkpoint 2.10 for additional placeholder requirements.

2.4 Allow time-independent interaction. (P1)

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.
2. The user agent may satisfy this checkpoint by pausing processing automatically to allow for user input, and resuming processing on explicit user request. When this technique is used, pause at the end of each time interval where user input is possible. In the paused state:
   • Alert the user that the rendered content has been paused (e.g., highlight the "pause" button in a multimedia player's control panel).
   • Highlight which enabled elements are time-sensitive.
   • Allow the user to interact with the enabled elements.
   • Allow the user to resume on explicit user request (e.g., by pressing the "play" button in a multimedia player's control panel; see also checkpoint 4.5).
3. The user agent may satisfy this checkpoint by generating a time-independent ("static") view, based on the original content, that offers the user the same opportunities for interaction. The static view should reflect the structure and flow of the original time-sensitive presentation; orientation cues will help users understand the context for various interaction opportunities.
4. When satisfying this checkpoint for a real-time presentation, the user agent may discard packets that continue to arrive after the construction of the time-independent view (e.g., when paused or after the construction of a static view).

Techniques for checkpoint 2.4

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. This checkpoint does not apply when the user agent cannot recognize the time interval in the presentation format, or when the user agent cannot control the timing (e.g., because it is controlled by the server). See also checkpoint 3.5, which involves client-driven content refresh.

2.5 Make captions, transcripts available. (P1)

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

For all content. Techniques for checkpoint 2.5

Content type labels: Video, Audio.

Note: This checkpoint is an important special case of checkpoint 2.1.

2.6 Respect synchronization cues. (P1)

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

Techniques for checkpoint 2.6

Content type labels: Video, Audio.

Note: This checkpoint is an important special case of checkpoint 2.1.

2.7 Repair missing content. (P2)

1. Allow configuration to generate repair text when the user agent recognizes that the author has failed to provide conditional content that was required by the format specification.
2. The user agent may satisfy this checkpoint by basing the repair text on any of the following available sources of information: URI reference, content type, or element type.

For all content. Techniques for checkpoint 2.7

Note: Some markup languages (such as HTML 4 [HTML4] and SMIL 1.0 [SMIL] require the author to provide conditional content for some elements (e.g., the "alt" attribute on the IMG element). Repair text based on URI reference, content type, or element type is sufficient to satisfy the checkpoint, but may not result in the most effective repair. Information that may be recognized as relevant to repair might not be "near" the missing conditional content in the document object. For instance, instead of generating repair text on a simple URI reference, the user agent might look for helpful information near a different instance of the URI reference in the same document object, or might retrieve useful information (e.g., a title) from the resource designated by the URI reference.

2.8 No repair text. (P3)

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

For all content. Techniques for checkpoint 2.8

Note: In some authoring scenarios, empty content (e.g., a string of zero characters) may make an appropriate text equivalent, such as when non-text content has no other function than pure decoration, or when an image is part of a "mosaic" of several images and doesn't make sense out of the mosaic. Please refer to the Web Content Accessibility Guidelines 1.0 [WCAG10] for more information about text equivalents.

2.9 Render conditional content automatically. (P3)

1. Allow configuration to render all conditional content automatically. The user agent is not required to render all conditional content at the same time in a single viewport.
2. Provide access to this content according to format specifications or where unspecified, by applying one of the techniques described in checkpoint 2.3: 1a, 2a, or 1b.

For all content. Techniques for checkpoint 2.9

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). The user agent may offer multiple configurations (e.g., a first configuration to render one type of conditional content automatically, a second to render another type, etc.).

2.10 Toggle placeholders. (P3)

1. Once the user has viewed the original author-supplied content associated with a placeholder, allow the user to turn off the rendering of the author-supplied content.

Techniques for checkpoint 2.10

Note: For example, if the user agent substitutes the author-supplied content for the placeholder in context, allow the user to "toggle" between placeholder and the associated content. Or, if the user agent renders the author-supplied content in a separate viewport, allow the user to close that viewport. Note: See checkpoint 2.3, provision (1b) for placeholder requirements.

2.11 Alert unsupported language. (P3)

1. Allow configuration not to render content in unsupported natural languages, when that content would otherwise be rendered. Content "in a natural language" includes pre-recorded spoken language and text in a given script, i.e., writing system.
2. Indicate to the user in context that author-supplied content has not been rendered.
3. This checkpoint does not require the user agent to allow different configurations for different natural languages.

Techniques for checkpoint 2.11

Note: For example, use a text substitute or accessible graphical icon to indicate that content in a particular language has not been rendered.

Ensure that the user may turn off rendering of content (audio, video, scripts, etc.) 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 (viewports that open, automatically redirected or refreshed pages, etc.) 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 may pose accessibility problems. Requirements for interactive control of rendered content are part of guideline 4.

Checkpoints

3.1 Toggle background images. (P1)

1. Allow configuration not to render background image content.
2. In this configuration, the user agent is not required to retrieve background images from the Web.
3. 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".

Techniques for checkpoint 3.1

Content type labels: Image.

Note: See checkpoint 2.3 for information about how to provide access to unrendered background images. When background images are not rendered, user agents should render a solid background color instead (see checkpoint 4.3).

3.2 Toggle audio, video, animated images. (P1)

1. Allow configuration not to render audio, video, or animated image content, except on explicit user request. This configuration is required for content rendered without any user interaction (including content rendered on load or as the result of a script), as well as content rendered as the result of user interaction (e.g., when the user activates a link).
2. The user agent may satisfy this checkpoint by making video and animated images invisible and audio silent, but this technique is not recommended.
3. 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.

Techniques for checkpoint 3.2

Content type labels: Animation, Video, Audio.

Note: See checkpoint 2.3 for information about how to provide access to unrendered audio, video, and animated images. See also checkpoint 4.5, checkpoint 4.9, and checkpoint 4.10.

3.3 Toggle animated/blinking text. (P1)

1. Allow configuration to render animated or blinking text content. as motionless, unblinking text. Blinking text is text whose visual rendering alternates between visible and invisible, any rate of change.
2. In this configuration, the user must still have access to the same text content, but the user agent may render it in a separate viewport (e.g., for large amounts of streaming text).
3. The user agent also satisfies this checkpoint by always rendering animated or blinking text as motionless, unblinking text.

Techniques for checkpoint 3.3

Content type labels: VisualText.

Note: 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). See also checkpoint 3.5. This checkpoint does not apply for blinking and animation effects that are caused by mechanisms that the user agent cannot recognize.

3.4 Toggle scripts. (P1)

1. Allow configuration not to execute any executable content (e.g., scripts and applets).
2. In this configuration, provide an option to alert the user when executable content is available (but has not been executed).
3. The user agent is only required to alert the user to the presence of more than zero scripts or applets (i.e., per-element alerts are not required).

Techniques for checkpoint 3.4

Note: This checkpoint does not refer to plug-ins and other programs that are not part of content. Scripts and applets may provide very useful functionality, not all of which causes accessibility problems. Developers should not consider that the user's ability to turn off scripts is an effective way to improve content accessibility; turning off scripts means losing the benefits they offer. Instead, developers should provide users with finer control over user agent or content behavior known to raise accessibility barriers. The user should only have to turn off scripts as a last resort.

3.5 Toggle content refresh. (P1)

1. Allow configuration so that the user agent only refreshes content on explicit user request.
2. In this configuration, alert the user of the refresh rate specified in content, and allow the user to request fresh content manually (e.g., by following a link or confirming a prompt).
3. When the user chooses not to refresh content, the user agent may ignore that content; buffering is not required.
4. This checkpoint only applies when the user agent (not the server) automatically initiates the request for fresh content.

Techniques for checkpoint 3.5

Note: For example, allow configuration to prompt the user to confirm content refresh, at the rate specified by the author.

3.6 Toggle redirects. (P2)

1. Allow configuration so that a "client-side redirect" (i.e., one initiated by the user agent, not the server) only changes content on explicit user request.
2. Allow the user to access the new content on demand (e.g., by following a link or confirming a prompt).
3. The user agent is not required to provide these functionalities for client-side redirects specified to occur instantaneously (i.e., after no delay).

Techniques for checkpoint 3.6

Note: Some HTML user agents support client-side redirects authored using a META element with http-equiv="refresh". Authors (and Web masters) should use the redirect mechanisms of HTTP instead.

3.7 Toggle images. (P2)

1. Allow configuration not to render image content.
2. The user agent may satisfy this checkpoint by making images invisible, but this technique is not recommended.

Techniques for checkpoint 3.7

Content type labels: Image.

Note: See checkpoint 2.3 for information about how to provide access to unrendered images.

Ensure that the user can select preferred styles (colors, size of rendered text, synthesized speech characteristics, etc.) 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 independently distinguishable audio tracks.

User agents with speech synthesis capabilities need to allow users to control various synthesized speech rendering parameters. For instance, users who are blind and hard of hearing 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.

Checkpoints for visually rendered text

4.1 Configure text size. (P1)

1. Allow global configuration of the reference size of visually rendered text, with an option to override reference sizes specified by the author or user agent defaults.
2. 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.

Techniques for checkpoint 4.1

Content type labels: VisualText.

Note: The reference size of rendered text corresponds to the default value of the CSS2 'font-size' property, which is 'medium' (refer to CSS2 [CSS2], section 15.2.4). For example, in HTML, this might be paragraph text. The default reference size of rendered text may vary among user agents. User agents may offer different mechanisms to allow control of the size of rendered text (e.g., font size control, zoom, magnification, etc.). Refer, for example to the Scalable Vector Graphics specification [SVG] for information about scalable rendering.

4.2 Configure font family. (P1)

1. Allow global configuration of the font family of all visually rendered text, with an option to override font families specified by the author or by user agent defaults.
2. 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.
3. For text that cannot be rendered properly using the user's preferred font family, the user agent may substitute an alternative font family.

Techniques for checkpoint 4.2

Content type labels: VisualText.

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)

1. Allow global configuration of the foreground and background color of all visually rendered text, with an option to override foreground and background colors specified by the author or user agent defaults.
2. 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.

Techniques for checkpoint 4.3

Content type labels: ColorText.

Note: User configuration of foreground and background colors may inadvertently lead to the inability to distinguish ordinary text from selected text, focused text, etc. See checkpoint 10.3 for more information about highlight styles.

Checkpoints for multimedia presentations and other presentations that change continuously over time

4.4 Slow multimedia. (P1)

1. Allow the user to slow the presentation rate of rendered audio and animations (including video and animated images).
2. For a visual track, provide at least one setting between 40% and 60% of the original speed.
3. 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. Below 80%, the user agent is not required to render the audio track.
5. The user agent is not required to satisfy this checkpoint for audio and animations whose recognized role is to create a purely stylistic effect.

Techniques for checkpoint 4.4

Content type labels: Animation, Audio.

Note: Purely stylistic effects include background sounds, decorative animated images, and effects caused by style sheets. The style exception of this checkpoint is based on the assumption that authors have satisfied the requirements of the "Web Content Accessibility Guidelines 1.0" [WCAG10] not to convey information through style alone (e.g., through color alone or style sheets alone). See checkpoint 2.6 and checkpoint 4.7.

4.5 Start, stop, pause, and navigate multimedia. (P1)

1. Allow the user to stop, pause, and resume rendered audio and animations (including video and animated images) that last three or more seconds at their default playback rate.
2. Allow the user to navigate efficiently within audio and animations (including video and animated images) that last three or more seconds at their default playback rate. The user agent may satisfy this requirement through forward and backward sequential access techniques (e.g., advance three seconds), or direct access techniques (e.g., play starting at the 10-minute mark), or some combination.
3. When serial techniques are used to satisfy the previous requirement, the user agent is not required to play back content during serial advance or rewind (though doing so may help orient the user).
4. The user agent is not required to satisfy this checkpoint for audio and animations whose recognized role is to create a purely stylistic effect.
5. When the user pauses a real-time audio or animation, the user agent may discard packets that continue to arrive during the pause.

Techniques for checkpoint 4.5

Content type labels: Animation, Audio.

Note: See checkpoint 4.4 for more information about the exception for purely stylistic effects. This checkpoint applies to content that is either rendered automatically or on request from the user. Respect synchronization cues per checkpoint 2.6.

4.6 Position captions. (P1)

1. For graphical viewports, allow the user to position rendered captions with respect to synchronized visual tracks as follows:
   • if the user agent satisfies this checkpoint by using a markup language or style sheet language to provide configuration or control, then the user agent must allow the user to choose from among at least the range of positions enabled by the format
   • otherwise the user agent must allow both non-overlapping and overlapping positions (e.g., by rendering captions in a separate viewport that may be positioned on top of the visual track).
2. In either case, the user agent must allow the user to override the author's specified position.
3. The user agent is not required to change the layout of other content (i.e., reflow) after the user has changed the position of captions.
4. The user agent is not required to make the captions background transparent when those captions are rendered above a related video track.

Techniques for checkpoint 4.6

4.7 Slow other multimedia. (P2)

1. Allow the user to slow the presentation rate of rendered audio and animations (including video and animated images) not covered by checkpoint 4.4.
2. The same speed percentage requirements of checkpoint 4.4 apply.

Techniques for checkpoint 4.7

Content type labels: Animation, Audio.

Note: User agents automatically satisfy this checkpoint if they satisfy checkpoint 4.4 for all audio and animations.

4.8 Control other multimedia. (P2)

1. Allow the user to stop, pause, resume, and navigate efficiently rendered audio and animations (including video and animated images) not covered by checkpoint 4.5.

Techniques for checkpoint 4.8

Content type labels: Animation, Audio.

Note: User agents automatically satisfy this checkpoint if they satisfy checkpoint 4.5 for all audio and animations.

Checkpoints for audio volume control

4.9 Global volume control. (P1)

1. Allow global configuration of the volume of all rendered audio, with an option to override audio volumes specified by the author or user agent defaults.
2. Allow the user to choose zero volume (i.e., silent).

Techniques for checkpoint 4.9

Content type labels: Audio.

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

4.10 Independent volume control. (P1)

1. Allow independent control of the volumes of rendered audio sources synchronized to play simultaneously.
2. The user agent is not required to satisfy this checkpoint for audio whose recognized role is to create a purely stylistic effect.
3. The user control required by this checkpoint includes the ability to override author-specified volumes for the relevant sources of audio.

Techniques for checkpoint 4.10

Content type labels: Audio.

Note: See checkpoint 4.4 for more information about the exception for purely stylistic effects. The user agent should satisfy this checkpoint by allowing the user to control independently the volumes of all audio sources (e.g., by implementing a general audio mixer type of functionality). See also checkpoint 4.13.

4.11 Control other volume. (P2)

1. Allow independent control of the volumes of rendered audio sources synchronized to play simultaneously that are not covered by checkpoint 4.10.

Techniques for checkpoint 4.11

Content type labels: Audio.

Note: User agents automatically satisfy this checkpoint if they satisfy checkpoint 4.10 for all audio.

Checkpoints for synthesized speech rendering

4.12 Configure synthesized speech rate. (P1)

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

Techniques for checkpoint 4.12

Content type labels: Speech.

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

4.13 Configure synthesized speech volume. (P1)

1. Allow control of the synthesized speech volume, independent of other sources of audio.
2. The user control required by this checkpoint includes the ability to override author-specified synthesized speech volume.

Techniques for checkpoint 4.13

Content type labels: Speech.

Note: See also checkpoint 4.10.

4.14 Configure synthesized speech characteristics. (P1)

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

Techniques for checkpoint 4.14

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: "adult male voice", "female child voice", "robot voice", "pitch", "stress", etc. Ranges for values may vary among speech synthesizers.

4.15 Specific synthesized speech characteristics. (P2)

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

Techniques for checkpoint 4.15

Note: This checkpoint is more specific than checkpoint 4.14: it requires support for the voice characteristics listed. Definitions for these characteristics are based on descriptions in section 19 of the Cascading Style Sheets Level 2 Recommendation [CSS2]; please refer to that specification for additional informative descriptions. Some speech synthesizers allow users to choose values for synthesized speech characteristics at a higher abstraction layer, i.e., by choosing from present options distinguished by "gender", "age", "accent", etc. Ranges of values may vary among speech synthesizers.

Content type labels: Speech.

4.16 Configure synthesized speech features. (P2)

1. Provide support for user-defined extensions to the synthesized speech dictionary, as well as the following functionalities:
   • spell-out: spell text one character at a time or according to language-dependent pronunciation rules;
   • speak-numeral: speak a numeral as individual digits or as a full number; and
   • speak-punctuation: speak punctuation literally or render as natural pauses.

Techniques for checkpoint 4.16

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

Checkpoints related to style sheets

4.17 Choose style sheets. (P1)

1. For user agents that support style sheets:
   • Allow the user to choose from and apply available author style sheets (in content).
   • Allow the user to choose from and apply available user style sheets.
   • Allow the user to ignore author and user style sheets.

Techniques for checkpoint 4.17

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

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

Control of viewport behavior is important to accessibility. For people with visual disabilities or certain types of learning disabilities, it is important that the point of regard – what the user is presumed to be viewing – remain as stable as possible. Unexpected changes may cause users to lose track of how many viewports are open, which viewport has the current focus, etc. This guideline includes requirements for control of opening and closing viewports, the relative position of graphical viewports, changes to focus, and inadvertent form submissions and micropayments.

Checkpoints

5.1 No automatic content focus change. (P2)

1. Allow configuration so that if a viewport opens without explicit user request, its content focus does not automatically become the current focus.
2. Configuration is preferred, but is not required if the content focus can only ever be moved on explicit user request.

Techniques for checkpoint 5.1

5.2 Keep viewport on top. (P2)

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.

Techniques for checkpoint 5.2

5.3 Manual viewport open only. (P2)

1. Allow configuration so that viewports only open on explicit user request.
2. 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).
3. Allow the user to close viewports.
4. If a viewport (e.g., a frame set) contains other viewports, these requirements only apply to the outermost container viewport.
5. Configuration is preferred, but is not required if viewports can only ever open on explicit user request.
6. 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.

Techniques for checkpoint 5.3

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 6.5 (for programmatic alert of changes to the user interface).

5.4 Selection and focus in viewport. (P2)

1. Ensure that when a viewport's selection or content focus changes, it is at least partially in the viewport after the change.

Techniques for checkpoint 5.4

Note: For example, if users navigating links move to a portion of the document outside a graphical viewport, the viewport should scroll to include the new location of the focus. Or, for users of audio viewports, allow configuration to render the selection or focus immediately after the change.

5.5 Confirm form submission. (P2)

1. Allow configuration to prompt the user to confirm (or cancel) any form submission.
2. Configuration is preferred, but it not required if forms can only ever be submitted on explicit user request.

Techniques for checkpoint 5.5

Note: For example, do not submit a form automatically when a menu option is selected, when all fields of a form have been filled out, or when a "mouseover" or "change" event occurs.

5.6 Confirm fee links. (P2)

1. Allow configuration to prompt the user to confirm (or cancel) any payment that results from activation of a fee link.
2. Configuration is preferred, but is not required if fee links can only ever be activated on explicit user request.

Techniques for checkpoint 5.6

5.7 Manual viewport close only. (P3)

1. Allow configuration to prompt the user to confirm (or cancel) closing any viewport that starts to close without explicit user request.

Techniques for checkpoint 5.7

Implement interoperable interfaces to communicate with other software (e.g., assistive technologies, the operating environment, plug-ins, etc.).

This guideline addresses interoperability between a conforming user agent and other software, in particular assistive technologies. The checkpoints of this guideline require implementation of application programming interfaces (APIs) for communication. There are three types of requirements in this guideline:

1. Requirements for what information must be communicated through an API.
2. Requirements for which APIs or types of APIs must be used to communicate this information.
3. Requirements for additional characteristics of these APIs.

Note: The User Agent Accessibility Guidelines Working Group believes that, in order to promote interoperability between a conforming user agent and more than one assistive technology, it is more important to implement conventional APIs than custom APIs, even though custom APIs may superior access. When conventional APIs do not allow users to satisfy the requirements of these checkpoints, however, developers may implement alternative APIs in order to conform to this document.

Checkpoints

6.1 DOM read access. (P1)

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:
   • the Core module for HTML;
   • the Core and XML modules for XML.

Techniques for checkpoint 6.1

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

6.2 DOM write access. (P1)

1. If the user can modify HTML and XML content through the user interface, provide the same functionality programmatically by conforming to the following modules of the W3C Document Object Model DOM Level 2 Core Specification [DOM2CORE] and exporting the interfaces they define:
   • the Core module for HTML;
   • the Core and XML modules for XML.

Techniques for checkpoint 6.2

Note: For example, if the user interface allows users to complete HTML forms, this must also be possible through the required DOM APIs. Please refer to the "Document Object Model (DOM) Level 2 Core Specification" [DOM2CORE] for information about HTML and XML versions covered.

6.3 Programmatic access to non-HTML/XML content. (P1)

1. For markup languages other than HTML and XML, provide programmatic read access to content.
2. Provide programmatic write access for those parts of content that the user can modify through the user interface. To satisfy these requirements, implement at least one API that is either
   • defined by a W3C Recommendation, or
   • a publicly documented API designed to enable interoperability with assistive technologies.
3. If no such API is available, or if available APIs do not enable the user agent to satisfy the requirements, implement at least one publicly documented API to satisfy the requirements, and follow operating environment conventions for the use of input and output APIs.
4. An API is considered available if the specification of the API is published (e.g., as a W3C Recommendation) in time for integration into a user agent's development cycle.

Techniques for checkpoint 6.3

Note: This checkpoint addresses content not covered by checkpoints checkpoint 6.1 and checkpoint 6.2.

6.4 Programmatic operation. (P1)

1. Provide programmatic read access to user agent user interface controls.
2. Provide programmatic write access for those controls that the user can modify through the user interface. For security reasons, user agents are not required to allow instructions in content to modify user agent user interface controls.
3. To satisfy these requirements, implement at least one API that is either
   • defined by a W3C Recommendation, or
   • a publicly documented API designed to enable interoperability with assistive technologies.
4. If no such API is available, or if available APIs do not enable the user agent to satisfy the requirements, implement at least one publicly documented API that allows programmatic operation of all of the functionalities that are available through the user agent user interface, and follow operating environment conventions for the use of input and output APIs.
5. An API is considered available if the specification of the API is published (e.g., as a W3C Recommendation) in time for integration into a user agent's development cycle.

For user agent features. Techniques for checkpoint 6.4

Note: APIs used to satisfy the requirements of this checkpoint may be platform-independent APIs such as the W3C DOM, conventional APIs for a particular operating environment, conventional APIs for programming languages, plug-ins, virtual machine environments, etc. User agent developers are encouraged to implement APIs that allow assistive technologies to interoperate with multiple types of software in a given operating environment (user agents, word processors, spreadsheet programs, etc.), as this reuse will benefit users and assistive technology developers. User agents should always follow operating environment conventions for the use of input and output APIs.

6.5 Programmatic alert of changes. (P1)

1. Provide programmatic alert of changes to content, user interface controls, selection, content focus, and user interface focus.
2. To satisfy these requirements, implement at least one API that is either
   • defined by a W3C Recommendation, or
   • a publicly documented API designed to enable interoperability with assistive technologies.
3. If no such API is available, or if available APIs do not enable the user agent to satisfy the requirements, implement at least one publicly documented API to satisfy the requirements, and follow operating environment conventions for the use of input and output APIs.
4. An API is considered available if the specification of the API is published (e.g., as a W3C Recommendation) in time for integration into a user agent's development cycle.

For both content and user agent. Techniques for checkpoint 6.5

Note: For instance, when user interaction in one frame causes automatic changes to content in another, provide a programmatic alert. This checkpoint does not require the user agent to alert the user of rendering changes caused by content (e.g., an animation effect or an effect caused by a style sheet), just changes to the content itself.

6.6 Conventional keyboard APIs. (P1)

1. Follow operating environment conventions when implementing APIs for the keyboard.
2. If such APIs for the keyboard do not exist, implement publicly documented APIs for the keyboard.

Techniques for checkpoint 6.6

Note: An operating environment may define more than one conventional API for the keyboard. For instance, for Japanese and Chinese, input may be processed in two stages, with an API for each.

6.7 API character encodings. (P1)

1. For an API implemented to satisfy requirements of this document, support the character encodings required for that API.

For both content and user agent. Techniques for checkpoint 6.7

Note: Support for character encodings is important so that text is not "broken" when communicated to assistive technologies. For example, the DOM Level 2 Core Specification [DOM2CORE], section 1.1.5 requires that the DOMString type be encoded using UTF-16. This checkpoint is an important special case of the other API requirements of this document.

6.8 DOM CSS access. (P2)

1. For user agents that implement Cascading Style Sheets (CSS), provide programmatic access to those style sheets in content by conforming to the CSS module of the W3C Document Object Model (DOM) Level 2 Style Specification [DOM2STYLE] and exporting the interfaces it defines.
2. For the purposes of satisfying this checkpoint, Cascading Style Sheets (CSS) are defined by either CSS Level 1 [CSS1] or CSS Level 2 [CSS2].

Techniques for checkpoint 6.8

Note: Please refer to the "Document Object Model (DOM) Level 2 Style Specification" [DOM2STYLE] for information about CSS versions covered.

6.9 Timely access. (P2)

1. Ensure that programmatic exchanges proceed in a timely manner.

For both content and user agent. Techniques for checkpoint 6.9

Note: For example, the programmatic exchange of information required by other checkpoints in this document should be efficient enough to prevent information loss, a risk when changes to content or user interface occur more quickly than the communication of those changes. Timely exchange is also important for the proper synchronization of alternative renderings. The techniques for this checkpoint explain how developers can reduce communication delays. This will help ensure that assistive technologies have timely access to the document object model and other information that is important for providing access.

Observe operating environment conventions for the user agent user interface, documentation, installation, etc.

Part of user agent accessibility involves following the conventions of the user's operating environment. This includes:

• following operating environment conventions for user agent user interface design, documentation, and installation.
• incorporating operating environment-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).

Following operating environment 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

7.1 Focus and selection conventions. (P1)

1. Follow operating environment conventions that benefit accessibility when implementing the selection, content focus, and user interface focus.

Techniques for checkpoint 7.1

Note: This checkpoint is an important special case of checkpoint 7.3. See also checkpoint 9.1 and checkpoint 9.2.

7.2 Respect input configuration conventions. (P1)

1. Ensure that default input configurations of the user agent do not interfere with operating environment accessibility conventions (e.g., for keyboard accessibility).

For user agent features. Techniques for checkpoint 7.2

Note: Information about operating environment accessibility conventions is available in the Techniques document [UAAG10-TECHS]. See also checkpoint 11.5.

7.3 Operating environment conventions. (P2)

1. Follow operating environment conventions that benefit accessibility. In particular, follow conventions that benefit accessibility for user interface design, keyboard configuration, product installation, and documentation.</