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, cognitive, and neurological). 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). Furthermore, all users, not just users with disabilities, should find conforming user agents to be more usable.

In addition to helping developers of HTML browsers and media players, 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 is the 17 December 2002 Recommendation of "User Agent Accessibility Guidelines 1.0." This document has been reviewed by W3C Members, the disability community, software developers, and other W3C groups and interested parties, and has been endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited as a normative reference from another document. W3C's role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.

This document was produced by the User Agent Accessibility Guidelines Working Group (UAWG). The goals of the UAWG are described in UAWG charter. The complete list of changes to this document is available on the Web.

The UAWG also provides additional resources to support this document (e.g., Frequently Asked Questions (FAQ) about UAAG 1.0, implementation reports, and test suites). Please consult the UAWG home page for more information.

Patent disclosures relevant to this specification may be found on the Working Group's patent disclosure page in conformance with W3C policy.

The list of errata for this document is available at http://www.w3.org/WAI/UA/UAAG-errata. Please report errors in this document to wai-uaag-editor@w3.org.

Please send other comments about this document to the public mailing list w3c-wai-ua@w3.org; public archives are available.

The English version of this document is the authoritative version. Translations into other languages may be available at http://www.w3.org/WAI/UA/UAAG-translations.

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.

A list of current W3C Recommendations and other technical documents can be found at the W3C Web site.

1. Introduction

This document specifies requirements that, if satisfied by user agent developers, will lower barriers to accessibility. This document includes the following:

• This introduction provides context for understanding the requirements listed in section 2.
• Section 2 explains 12 general principles of accessible design, called "guidelines." Each guideline consists of a list of requirements, called "checkpoints," which must be satisfied in order to conform to this document. Note: Section 2 is numbered differently than the other sections; it consists of a list of guidelines. In section 2, "checkpoint 1.2" refers to the second checkpoint of the first guideline. "Section 1.2" refers to a subsection of the Introduction.
• Section 3 explains how to make claims that software components satisfy the requirements of section 2.
• An appendix offers a summary of this document's principal goals and structure [UAAG10-SUMMARY].
• A second appendix lists all the checkpoints for convenient reference (e.g., as a tool for developers to evaluate software for conformance) [UAAG10-CHECKLIST].

A separate document, entitled "Techniques for User Agent Accessibility Guidelines 1.0" (the "Techniques document" from here on) [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 in the Techniques document are informative examples only, and other strategies may be used or required to satisfy the checkpoints. The UAWG expects to update the Techniques document more frequently than the current guidelines. Developers, W3C Working Groups, users, and others are encouraged to contribute techniques.

1.1 Relation 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. The accessibility-related interests of these stakeholders intersect and complement each other as follows:

• Designers of formats (e.g., HTML, XHTML, XML, SVG, SMIL, MathML, and XForms) and protocols (e.g., HTTP) create specifications that allow communication on the Web. Format designers include features in these specifications that authors should use to create accessible content and that user agents should support through an accessible user interface. The "XML Accessibility Guidelines (XAG)" [XAG10] explains the responsibilities of XML format designers; many XAG requirements make sense for non-XML formats as well.
• Authors make use of the accessibility features of different format specifications, use markup appropriately, write in clear and simple language, and organize a Web site consistently. The "Web Content Accessibility Guidelines 1.0" [WCAG10] explains the responsibilities of authors in meeting the needs of users with disabilities. The "Web Content Accessibility Guidelines (WCAG) 1.0" is considered within UAAG 1.0 to be the reference set of requirements to make Web content accessible. 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 meets the needs of users with disabilities through conformance to other specifications, an accessible user interface, accessible documentation, and communication with other software (notably assistive technologies).

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 8.1 requires implementation of the accessibility features of specifications. Features are those identified as such and those that satisfy all of the requirements of WCAG 1.0 [WCAG10].
• UAAG 1.0 checkpoint 12.1 requires conformance to WCAG 1.0 for user agent documentation.
• UAAG 1.0 also incorporates some terms and concepts from WCAG 1.0, a consequence of fact that the documents were designed to complement one another.

Some requirements of this document take into account limitations of formats, authors, and designers. For example, formats generally do not enable authors to encode all of their knowledge in a way that a user agent can fully 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 of these limitations are taken into account as follows:

• 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 2.7 and checkpoint 2.10) for cases where content does not conform to WCAG 1.0. Furthermore, this document includes some requirements to address certain widespread authoring practices that are discouraged because they may 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 (WCAG 1.0, checkpoint 14.1). See the section on checkpoint applicability for more information about what the user agent is expected to recognize.

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.

Note: The Web Accessibility Initiative is developing new versions of both the Web Content Accessibility Guidelines and the Authoring Tool Accessibility Guidelines. The User Agent Accessibility Guidelines Working Group expects to follow the progress of those documents. UAAG 1.0 refers only to the WCAG 1.0 and ATAG 1.0 Recommendations, which will remain available and unchanged.

1.2 Target user agents

This document was designed specifically to improve the accessibility of user agents with multimedia capabilities running in the following type of environment (typically that of a desktop computer):

• The operating environment includes a keyboard (or keyboard equivalent)
• Assistive technologies may be used in the operating environment and may communicate with the conforming user agent

The target user agent is one designed for the general public to handle general-purpose content in ordinary operating conditions.

This document does not forbid conformance by other types of user agents, but some requirements (e.g., implementation of certain application programming interfaces, or APIs) are not likely to be satisfied in environments (e.g., handheld devices or kiosks) other than the target environment. Future work by the UAWG may address the accessibility of user agents running on handheld devices, for example.

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.

1.2.1 Composition of conforming user agents

In general, a conforming user agent will consist of several coordinated components, such as a Web browser, a multimedia player, several plug-ins, features or applications provided by the operating environment, and documentation distributed with the software or available on the Web. These components may run on the user's computer or on a server. A conforming user agent may also include assistive technologies and applications provided by the operating environment. The current document places no restrictions on the type or number of components used for conformance.

This does not mean that every component that one has chosen as part of the user agent has to satisfy every single requirement; some requirements may not be relevant for a particular component. For instance, if a component does not have a user interface, the user interface requirements would not be relevant. On the other hand, if a component has a user interface, the user interface requirements are relevant. Conformance addresses the composite user agent as a whole.

1.2.2 Use of operating environment features

The UAWG encourages developers to satisfy the requirements of this document by adopting operating environment conventions and features that benefit accessibility. When an operating environment feature (e.g., the operating system's audio control panel, including its user interface) is adopted to satisfy the requirements of this document, it is part of the user agent.

See additional information on conformance of user agents running in multiple operating environments.

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 speak.
• May not be able to perceive, read, or process some types of information easily or at all.
• May not have or be able to use a keyboard or pointing device.

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

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., the checkpoints of guideline 7 and guideline 11) but 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 rendering with groups in W3C's Voice Browser Activity and Multimodal Interaction Activity.

Output modalities

This document does not include requirements for braille rendering. Some requirements are specific to graphical rendering and others specific to audio output or synthesized speech output. Speech rendering requirements are made by checkpoint 4.9 to checkpoint 4.13. Many of the requirements of this document are generic enough to apply to a variety of output modalities, including braille. User agents conform to this document by supporting some combination of graphical and audio/speech rendering output; see the section on Content type labels for more information.

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 (e.g., images).

Note: A user agent may implement resizing functionalities as part of conformance to other specifications (e.g., Scalable Vector Graphics [SVG]).

Background image interference

The requirement of checkpoint 3.1 to allow the user to turn off rendering of background images does not extend to multi-layered rendering.

User control of every user interface component

This document distinguishes user interface features that are part of the user agent user interface and those that are part of content. Some checkpoints (e.g., those in guideline 5) require user control over rendering and behavior that is driven by content only. This document does not always explicitly require the same control over features of the user agent user interface. Nevertheless, this document (see checkpoint 7.3) does require user agents to follow software usability guidelines. The UAWG expects such usability guidelines to include requirements for user control over user interface behavior.

Note: It is more difficult for users to distinguish content from user interface when both are rendered as sound in one temporal dimension, than it is when both are rendered visually in two spatial dimensions. Thus, the UAWG encourages developers of user agents that include audio output or synthesized speech output to apply the requirements of this document to both content and user agent components.

Time parameters

This document includes requirements (see checkpoints 2.4, 4.4, 4.5, and 4.9) for control of some time parameters. The requirements are for time parameters that the user agent recognizes and controls. This document does not include requirements for control of time parameters managed on the server.

Digital rights management

The User Agent Accessibility Guidelines Working Group recognizes that further work is necessary in the area of digital rights management as it relates to accessibility. Digital rights management refers to methods of describing and perhaps enforcing intellectual property associated with Web resources.

Note: The User Agent Accessibility Guidelines Working Group may address these and other topics in a future version of the User Agent Accessibility Guidelines. Even though UAAG 1.0 does not address these topics, the UAWG encourages user agent developers to consider them in their designs.

1.4 Relation to general software design guidelines and other specifications

One the goals of the authors of this document is to ensure that the requirements 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 document [UAAG10-TECHS] includes some references to general software design guidelines and platform-specific accessibility guidelines (in particular, see checkpoint 7.3). Involving people with disabilities in the design and testing of software will generally improve the accessibility of the software.

This document promotes conformance to other specifications as part of accessible design. Conformance to specifications makes it easier to design assistive technologies, and helps ensure the implementation of built-in accessibility functions.

This document also includes some requirements to implement an accessibility feature that may only be optional in another specification.

In rare cases, a requirement in UAAG 1.0 may conflict with a requirement in another specification. UAAG 1.0 does not define a process for resolving such conflicts. The authors of this document anticipate that developers will consider accessibility implications in determining how to resolve them.

1.4.1 Installation

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. Furthermore, the installation procedure should provide and install all components necessary to satisfy the requirements of this document, since the risk of installation failure increases with the number of components (e.g., plug-ins) to be installed.

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 (e.g., user interface, documentation, and operating environment conventions) are already covered by the complete set of checkpoints.

1.5 Security considerations

Some of the requirements of this document may have security implications, such as communication through APIs, and allowing programmatic read and write access to content and user interface control. This document assumes that features required by this document will be built on top of an underlying security architecture. Consequently, unless permitted explicitly in a checkpoint (as in checkpoint 6.5), this document grants no conformance exemptions based on security issues.

Developers should design user agents that enable communication with trusted assistive technologies. Sensitive information that the user agent can access through the user agent's user interface should also be available to assistive technologies through secure means. For instance, if the user types a password in the user agent user interface, do not communicate substitute characters (such as asterisks) through an API, but rather the real password, properly encrypted.

Note also that appropriate user agent behavior with respect to security may depend on the user's context. For instance, hiding typed passwords with asterisks is much less important for someone alone in a room than for someone in a crowded room. Similarly, while unencrypted passwords rendered as synthesized speech should not be broadcast in a crowded room, they may pose no security risk if the user is wearing an earphone.

For information related to security, refer to "XML-Signature Syntax and Processing" [XMLDSIG] and "XML Encryption Syntax and Processing" [XMLENC].

1.6 User control

This document emphasizes the goal of ensuring that users, including users with disabilities, have control over their environment for accessing the Web. Key methods for achieving that goal include: optional self-pacing, configurability, device-independence, interoperability, direct support for both graphical and auditory output, and adherence to published conventions. Chapter 2 addresses these issues in detail.

This document also acknowledges the importance of author preferences and the proper implementation of specifications. However, this document includes requirements to override certain author preferences when the user would not otherwise be able to access that content.

1.6.1 Control of automatic behavior

Many of the requirements in this document give the user additional control over behavior that would otherwise occur automatically. For instance, there is a requirement to allow configuration to not open a viewport automatically (checkpoint 5.3) and one that requires user confirmation before submitting a form (checkpoint 5.5). This type of manual configuration option may be essential for some users with disabilities, since automatic behavior may be disorienting or interfere with navigation.

1.6.2 Configurability

This document includes requirements for users with a variety of disabilities, in part because some users may have more than one disability. In some cases, it may appear that two requirements contradict each other. For instance, a user with a physical disability may prefer that the user agent offer more automatic behavior (to reduce demand for physical effort) than a user with a cognitive disability (for whom automatic behavior may cause confusion). Thus, many of the requirements in this document involve configuration as one way to ensure that a functionality designed to improve accessibility for one user does not interfere with accessibility for another. Also, since a default user agent setting may be useful for one user but interfere with accessibility for another, this document prefers configuration requirements to requirements for default settings. Finally, there may be some cases where, for some content, a feature required by this document is ineffective or causes content to be less accessible, making it imperative that the user be able to turn off the feature.

To avoid overwhelming users with an abundance of configuration options, this document includes requirements that promote ease of configuration and documentation of accessibility features (see guideline 12).

1.6.3 Device independence, spatial independence, and temporal independence

Many requirements in this document promote different kinds of independence:

• Input and output device independence. This document includes some requirements to promote device-independence natively, as well as requirements for interoperability with assistive technologies that provide complementary input and output functionalities.
• Spatial independence. Some users may not navigate effectively in two-dimensional visual space (e.g., users who do not use a pointing device) or may be constrained to one temporal dimension (e.g., users of audio-only output).
• Temporal independence. Some users (e.g., users with a physical or cognitive disability) may not be able to interact with content that changes over time, or interaction with content that is time-sensitive.

1.6.4 Additional benefits of accessible user agent design

In meeting the goals of users with disabilities, user agent developers will also improve access to the Web for users in general. For example, users without disabilities:

• 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.
• may be in a situation where their eyes, ears, or hands are busy or interfered with (e.g., driving to work or working in a noisy environment). 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.
• 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.

The UAWG expects that software which satisfies the requirements of this document will 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 12 guidelines in this document state general principles for the development of accessible user agents. Each guideline includes:

• The guideline number.
• The guideline title. (Informative)
• A slightly longer statement of what the guideline addresses. (Informative)
• The rationale behind the guideline and identification of some groups of users who benefit from it. (Informative)
• 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, but rather is a phrase to help readers remember an important requirement made by the checkpoint provision(s). (Informative)
• The priority of the checkpoint. (Normative)
• A link to the Techniques document [UAAG10-TECHS] for more information about the checkpoint: rationale, who benefits, example techniques, references, and more. (Informative)
• A list of one or more checkpoint provisions, which embody the requirements of the checkpoint. These requirements must be satisfied by the user agent for conformance. (Normative)
• Techniques that are sufficient for satisfying all or part of a checkpoint. (Normative when present)
• Normative inclusions and exclusions. These are qualifications about what is required (inclusion) or is not required (exclusion) to satisfy the checkpoint. Some of the inclusions are reminders about what may be required for conformance:
  1. When it might be ambiguous whether a checkpoint makes requirements for content only, the user agent user interface only, or both together, a label will state the intended scope. See the section on requirements for content, user agent features, or both for more information.
  2. When a checkpoint may be excluded from a conformance profile, it is identified by a conformance profile label. See the section on conformance profiles for more information on how a user agent may conform to this document even though it does not satisfy every checkpoint.
  (Normative when present)
• Notes about the checkpoint (beginning with the word "Note"). The notes clarify the scope of the checkpoint through further description, examples, cross references, and commentary. (Informative when present)

The UAWG encourages first-time readers of this document to take advantage of 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.

About the checkpoints

By design, the checkpoints in this document are generally technology-independent so that they make sense for a variety of existing and future technologies. The Techniques document [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.

Each checkpoint is a "minimal" requirement that must be satisfied for conformance. Developers can always implement features beyond those required by this document. In some cases, it may be easier (or just better design) to implement a general feature rather than one that meets only the narrow requirement of a single checkpoint. For example, a navigable structure view of content that allows users to query elements for their properties is likely to benefit all users and may 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 so that, through the keyboard, ..."

In general, each provision makes a single requirement. However, some provisions include more than one requirement in order to emphasize an important relationship. For instance, checkpoint 4.4 includes requirements that apply to both audio and animations in order to emphasize a particular property of content that changes continuously over time. When a provision includes more than one requirement, it is possible that only certain "portions" of the provision will be relevant to a chosen conformance profile; this is illustrated in an example of building a conformance profile.

Priorities

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

Priority 1 (P1)

If the user agent does not satisfy this checkpoint, 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)

If the user agent does not satisfy this checkpoint, 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)

If the user agent satisfies this checkpoint, one or more groups of users with disabilities will find it easier to access the Web.

This document uses the priorities as one mechanism for allowing conformance to well-defined sets of checkpoints. See the section on conformance levels for more information.

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).

Though it may seem contradictory, 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, 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 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

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

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 a "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 Activate event handlers (P1) Techniques for checkpoint 1.2

1. Allow the user to activate, through keyboard input alone, all input device event handlers that are explicitly associated with the element designated by the content focus.
2. In order to satisfy provision one of this checkpoint, the user must be able to activate as a group all event handlers of the same input device event type. For example, if there are 10 handlers associated with the onmousedown event type, the user must be able to activate the entire group of 10 through keyboard input alone, and must not be required to activate each handler separately.

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

1.3 Provide text messages (P1) Techniques for checkpoint 1.3

1. Ensure that every message (e.g., prompt, alert, or notification) that is a non-text element and is part of the user agent user interface has a text equivalent.

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.

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:

• 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 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 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

1. Allow configuration to provide access to each piece of unrendered conditional content "C".
2. 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 allowing the user to query 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); and
     • (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; and
     • (3b) allow the user to follow a link in context to C.

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).

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 3.5, 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 1.0 [WCAG10] 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 background image content.

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 (P1) Techniques for checkpoint 3.2

1. Allow configuration not to render audio, video, or animated image content, except on explicit user request.

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.

3.3 Toggle animated or blinking text (P1) Techniques for checkpoint 3.3

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, at any rate of change.

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).

3.4 Toggle scripts (P1) Techniques for checkpoint 3.4

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

Note: 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 automatic content retrieval (P1) Techniques for checkpoint 3.5

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."

3.6 Toggle images (P2) Techniques for checkpoint 3.6

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 1.0" [WCAG10] not to convey information through style alone (e.g., through color alone or style sheets alone).

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.