Web Content Accessibility Guidelines 2.0

W3C Working Draft 01 June 2005

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Ben Caldwell, Trace R&D Center
Wendy Chisholm, W3C
Gregg Vanderheiden, Trace R&D Center
Jason White, University of Melbourne


The World Wide Web Consortium (W3C) published the Web Content Accessibility Guidelines 1.0 (WCAG 1.0) as a Recommendation in May 1999. This Working Draft for version 2.0 builds on WCAG 1.0. It has the same aim: to explain how to make Web content accessible to people with disabilities and to define target levels of accessibility. Incorporating feedback on WCAG 1.0, this Working Draft of version 2.0 focuses on guidelines. It attempts to apply guidelines to a wider range of technologies and to use wording that may be understood by a more varied audience.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document is prepared by the Web Content Accessibility Guidelines Working Group (WCAG WG) to show how more generalized (less HTML-specific) WCAG guidelines might read. This draft is not yet based on consensus of the WCAG Working Group nor has it gone through W3C process. This Working Draft in no way supersedes WCAG 1.0.

Please refer to "Issue Tracking for WCAG 2.0 Working Draft" for a list of open issues related to this Working Draft. The "History of Changes to WCAG 2.0 Working Drafts" is also available.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress. A list of current W3C Recommendations and other technical documents is available.

The Working Group welcomes comments on this document at public-comments-wcag20@w3.org. The archives for this list are publicly available. Archives of the WCAG WG mailing list discussions are also publicly available.

This document was produced under the 5 February 2004 W3C Patent Policy. The Working Group maintains a public list of patent disclosures relevant to this document; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) with respect to this specification should disclose the information in accordance with section 6 of the W3C Patent Policy.

This document has been produced as part of the W3C Web Accessibility Initiative (WAI). The goals of the WCAG WG are discussed in the Working Group charter. The WCAG WG is part of the WAI Technical Activity.

Table of Contents




This document outlines design principles for creating accessible Web content. When these principles are ignored, individuals with disabilities may not be able to access the content at all, or they may be able to do so only with great difficulty. When these principles are employed, they also make Web content accessible to a variety of Web-enabled devices, such as phones, handheld devices, kiosks, network appliances. By making content accessible to a variety of devices, that content will also be accessible to people in a variety of situations.

The design principles in this document represent broad concepts that apply to all Web-based content. They are not specific to HTML, XML, or any other technology. This approach was taken so that the design principles could be applied to a variety of situations and technologies, including those that do not yet exist.

How to read this document

In order to facilitate understanding of the guidelines and to help people focus in on just the parts they need, the guidelines are presented as a set of interrelated documents. There are 3 layers to the guidelines information.

1 - Top layer - Overview of Design Principles, Guidelines, Success Criteria

The top layer is titled "Web Content Accessibility Guidelines 2.0". It is the document you are currently reading. This document provides:

  1. An introduction

  2. The 4 major principles for accessibility (Perceivable, Operable, Understandable and Robust).

  3. The (non-technology-specific) guidelines (13 in total).

  4. Success criteria (normative), and definitions, benefits and examples (all non-normative) for each guideline

  5. An appendix containing definitions, references and other support information.

2 - Technology-specific Checklists

In addition to the general guidelines, there will be a series of technology-specific checklist documents. These documents will provide information on what is required when using different technologies in order to meet the WCAG 2.0 Working Draft.

Editorial Note: These checklists do not yet exist. At the present time, it is not clear if the checklists will be normative or non-normative. If checklists are non-normative, it is easier to update them. If checklists are normative, changes made to them alter the definition of conformance. However, it may be necessary to make checklists normative in order for the guidelines to be testable.

3 - Bottom layer - Technology-specific application information

The Techniques Documents will include code examples, screen shots, and other information specific to a technology. These documents will be non-normative. They will contain different strategies for meeting the requirements as well as the current preferred approaches, where they exist. Examples include:

(Items above will become active links as the corresponding Working Drafts are published)


These guidelines have been written to meet the needs of many different audiences, from policy makers, to managers, to those who create Web content, to those who write the code. Every attempt has been made to make the document as readable and usable as possible while still retaining the accuracy and clarity needed in a technical specification. For first time users, the work of the Education and Outreach Working Group of the Web Accessibility Initiative is highly recommended. In particular, Getting Started: Making a Web Site Accessible.

Authoring tools

A large part of Web content is created using authoring tools. These tools often determine how Web content is implemented, either by making authoring decisions directly or by limiting the choices available to the author. As a result, authoring tools will play an important role in creating Web content that conforms to the Web Content Accessibility Guidelines. At the same time, we recommend that all authors become familiar with the Guidelines because this will help in creating accessible content and coverage of the Guidelines may vary between tools.

Developers of authoring tools can help to make their tools more aware of the Web Content Accessibility Guidelines by following the Authoring Tool Accessibility Guidelines.

We encourage users and purchasers of authoring tools to consider conformance to the Authoring Tool Accessibility Guidelines as a criterion when selecting tools.

Editorial Note: The Authoring Tool Accessibility Guidelines Working Group has published Working Drafts of ATAG 2.0. The above references will need to be updated as ATAG 2.0 moves through recommendation track.


These guidelines cover a wide range of issues and recommendations for making Web content more accessible. They include recommendations to make content accessible and usable by people with a full range of disabilities. In general, the guidelines do not include standard usability recommendations except where they have specific ramifications for accessibility.

Priorities and Techniques

This Working Draft of WCAG 2.0 builds upon WCAG 1.0 and reflects feedback received since the publication of WCAG 1.0 in May 1999. Although the same approaches to accessibility are followed in 1.0 and 2.0, the organization and structure have changed. Where WCAG 1.0 uses guidelines to group checkpoints, this Working Draft of WCAG 2.0 uses guidelines to group success criteria. Where WCAG 1.0 assigns a priority to a checkpoint, this Working Draft of WCAG 2.0 categorizes a success criterion into one of three levels.

In addition, the general design principles have been reworded to apply across a wide range of existing and emerging technologies. The WCAG 2.0 Working Draft does not include technology-specific implementation requirements or techniques, but it will link to technology-specific requirements as well as technology-specific examples and techniques (as soon as those documents are more stable).

The Web Content Accessibility Guidelines Working Group is working to ensure that organizations and individuals who are currently using WCAG 1.0 (which remains stable and referenceable at this time) will be able to smoothly transition to WCAG 2.0. For more information about the similarities and differences between WCAG 1.0 Checkpoints and WCAG 2.0 Guidelines and success criteria, please refer to the (draft) Mapping Between WCAG 1.0 and the WCAG 2.0 Working Draft.


Editorial Note: Baseline Technologies Assumption

In working on WCAG 2.0, the WCAG WG continues to struggle with the role of content authors and the role of user agents in making Web content accessible to people with disabilities. In WCAG 1.0, we identified shortcomings in user agents and created guidelines with phrases like, "until user agents..."

Today, many of the same issues continue to exist but we are looking for a more effective mechanism to address them than creating "temporary bridge" guidelines designed to make up for user agent shortcomings. One way of doing this would be to write the guidelines based on an assumption of a baseline user agent. We are currently considering using user agents that conform to the User Agent Accessibility Guidelines 1.0 as the baseline User Agent for WCAG 2.0. That is, the WCAG 2.0 guidelines would be written assuming that all users had user agents that conform to all of the priority 1 checkpoints from the User Agent Accessibility Guidelines 1.0 (UAAG 1.0). This has many implications. For example, WCAG 2.0 would assume that user agents and assistive technologies can effectively interact with scripted content.

Today, no single user agent meets all of the UAAG 1.0 priority 1 checkpoints. If WCAG 2.0 adopts an assumption that user agents conform to UAAG 1.0 priority 1 checkpoints, there would be some shortfall between Web content that meets WCAG 2.0 and currently available user agents. To address this shortfall, we propose to take two measures.

  1. Press hard for the development of user agents that conform to all priority 1 checkpoints of UAAG 1.0

  2. Develop a set of "repair techniques" that could be used by content authors who would like to create content that not only meets WCAG 2.0, but that also makes up for the shortfall in current user agents.

We would also like to work with the User Agent Accessibility Guidelines Working Group (UAWG) and Authoring Tools Accessibility Guidelines Working Group (AUWG) to come up with a set of strategies that user agent manufacturers could build into user agents to help make up for common errors of content authors.

The result would be a more stable WCAG 2.0 as well as better integration with UAAG to put the responsibility for the appropriate parts of the accessibility issue on the appropriate parts of the Web technologies (user agents versus Web content). Refer to Interdependent Components of Web Accessibility for more information.

The WCAG working group is analyzing this approach to understand better how it might affect users. The guidelines and success criteria in this working draft do not yet reflect this direction. The WCAG WG invites you to comment on this approach and the related issues.

Editorial Note: There are several open issues with the proposed conformance scheme. This section outlines the conformance scheme used throughout this document. Feedback, comments, and proposals are encouraged.

Success criteria for every guideline are categorized into three levels:

  • Level 1 success criteria:

    1. Achieve a minimum level of accessibility through markup, scripting, or other technologies that interact with or enable access through user agents, including assistive technologies

    2. Can reasonably be applied to all Web resources.

  • Level 2 success criteria:

    1. Increase accessibility through one or both of the following:

      1. further facilitating the ability of user agents to provide accessible content

      2. recommending content and/or presentation that provides direct accessibility without requiring users who have disabilities or their user agents to do anything different from users without disabilities or their user agents

    2. Can reasonably be applied to all Web resources.

  • Level 3 success criteria:

    1. Go beyond Level 1 and 2 to increase direct and user agent enhanced accessibility.

The Working Group believes that all success criteria should be testable. Tests can be done by computer programs or by people who understand these guidelines. Tests done by people who understand the guidelines should get the same results testing the same content for the same success criteria.

Editorial Note: To facilitate discussion related to the levels assigned to each criterion, a square bracket notation is included at the end of each criterion. "[I]" (invisible) indicates that a criterion does not specify how information is presented and "[V]" (visible) indicates that addressing the criterion may require an author to present content in particular ways.


Some guidelines do not contain level 1 success criteria.

Conformance Requirements

WCAG 2.0 defines accessibility guidelines and success criteria as functional outcomes that are technology independent to allow conformance using any Web technology that supports accessibility. WCAG 2.0 therefore does not require or prohibit the use of any specific technology. It is possible to conform to WCAG 2.0 using W3C and non-W3C technologies, provided they are supported by accessible user agents. In choosing technologies to rely upon, developers need to know what technologies they can assume are supported by accessible user agents. This is called the baseline.

Developers must ensure that all information and functionality comprising the Web content conforms to WCAG assuming user agents support only the technologies in the chosen baseline. Developers may also use technologies that are not in the chosen baseline provided that the following are true:

  1. The Web content still conforms using user agents that only support the technologies that are in the baseline (i.e. the use of technologies that are not in the baseline does not "break" access to the Web content by user agents that don't support them.)

  2. All content and functionality must be available using only the baseline technologies.

  3. Baselines may be defined outside the WCAG 2.0 guidelines as part of a more comprehensive accessibility policy. Baseline considerations will be significantly different if the organization defining the baseline can guarantee the user agents used by the users.

For example, a company or government agency provides its employees with the information technology tools they need to do their jobs. So for intranet sites used only by employees, it is reasonable for the baseline to include newer technologies that might only be supported in one user agent as long as the organization provides that user agent to its employees.

For a government publishing information for its citizens on the Internet, however, it is reasonable for the baseline to only include technologies that have been widely supported by more than one accessible user agent for more than one release.

Alternatively, governments might implement funding policies to provide citizens with accessible user agents that support newer technologies. In this case, it is reasonable for governments to include in their baseline newer technologies that have limited support by accessible user agents.

  1. Any conformance with WCAG 2.0 requires that all level 1 success criteria for all guidelines be met assuming user agent support for only the technologies in the chosen baseline.

  2. WCAG 2.0 conformance at level A means that all level 1 success criteria for all guidelines are met assuming user agent support for only the technologies in the chosen baseline.

  3. WCAG 2.0 conformance at level Double-A means that all level 1 and all level 2 success criteria for all guidelines are met assuming user agent support for only the technologies in the chosen baseline.

  4. WCAG 2.0 conformance at level Triple-A means that all level 1, level 2 and level 3 success criteria for all guidelines are met assuming user agent support for only the technologies in the chosen baseline.

The Working Group believes that success criteria at all 3 levels are important or essential for some people. Thus, the old descriptions of "impossible to access" for Level A, "difficult to access" for Level AA, and "somewhat difficult" for Level AAA are no longer used. Instead we define the three levels as above.

Conformance Claims

All conformance claims must include at least the following information:

  1. The version of the guidelines to which the conformance claim is made.

  2. A list of one or more URIs or URI patterns, identifying the delivery units for which the claim is made. A resource conforms to WCAG 2.0 at a given conformance level only if all content provided by that resource so conforms.


    If multiple representations can be retrieved from a URI through content negotiation, then the conformance claim would be for the delivery unit that is returned when no negotiation is conducted (unless the server returns an error for that condition in which case one of the negotiated forms must comply).

    Editorial Note: There is some question as to whether URI is specific enough a reference to the material for which the claim is being made.

  3. The level of conformance being claimed.

Editorial Note: A question has been raised as to whether the information required in items 1-3 above should all be transmitted in the HTTP header or in some other way.

Level of conformance being claimed

The conformance level for a delivery unit that contains authored units is equal to the lowest conformance level claimed for the delivery unit content and any of the authored units it contains - including claims of aggregated units.

A resource referred to by a URI conforms to WCAG 2.0 at a given conformance level only if all content provided by that resource so conforms. For example, if the resource provides information retrieved from a database in response to users' queries, all delivery units containing such information must satisfy the success criteria of WCAG 2.0 to the level at which conformance is claimed. Note that an exception arises if content negotiation is in effect and the user agent requests a version of the content that does not meet WCAG 2.0 at the asserted conformance level.

Editorial Note: We are currently looking at how to handle unknown or community-contributed, authored units that are created using an aggregator supplied tool. If the aggregator-supplied tool conforms to ATAG, can ATAG conformance be used to imply that the aggregated content conforms to WCAG?

Scoping of Conformance Claims

Conformance claims can be scoped to pertain to only some parts of a Web site. All conformance claims, however, must be directed to a URI or a range of URIs. Scoping to exclude a particular type of content (for example, images or scripts) from a site is not allowed since it would allow exclusion of individual success criteria. Scoping by URI to exclude sections of a site is allowed so that authors can make claims for just some parts of a site.

Content that conforms to WCAG 1.0

Authors that have content that currently conforms to WCAG 1.0 that want to transition to WCAG 2.0 over time may want to capitalize on past accessibility efforts. A qualified conformance statement could allow them this flexibility. For example, a conformance claim might include the following statement, "Materials created or modified before 24 April 2003 conform to WCAG 1.0. Materials created or modified on or after 24 April 2003 conform to WCAG 2.0. If a delivery unit is modified in a significant way then the full delivery unit should conform to WCAG 2.0."

Editorial Note: In some instances, the WCAG 2.0 Working Draft may be easier to conform to than the WCAG 1.0 Recommendation while other criteria might be harder to meet in WCAG 2.0 than in WCAG 1.0. The WCAG WG will consider the differences between WCAG 1.0 and WCAG 2.0 conformance and offer advice to developers who currently conform to WCAG 1.0. This advice might take the form of a WCAG 1.0 conformance profile to WCAG 2.0 and information about migrating from WCAG 1.0 to WCAG 2.0. This advice is not yet available.

Overview of Design Principles

The overall goal is to create Web content that is perceivable, operable and understandable by the broadest possible range of users and compatible with a wide range of assistive technologies, now and in the future. The basic principles include:

  1. Content must be perceivable.

  2. Interface elements in the content must be operable.

  3. Content and controls must be understandable.

  4. Content must be robust enough to work with current and future technologies.

Accessible Web content benefits a variety of people, not just people with disabilities. In the physical world, ramps are used by people riding bicycles or pushing baby strollers as well as people in wheelchairs. Similarly, accessible Web content is beneficial to a variety of people with and without disabilities. For example, people who are temporarily operating under constrained conditions such as extremely noisy environments or poor lighting would benefit from accessible content. Likewise, someone using a search engine can find a famous line in a movie if the movie has been captioned to support users who are hard of hearing.


These principles apply only to Web content presented to a human reader. A structured database or metadata collection where the data is intended for use by another machine, and that requires no interface, lies outside the scope of these guidelines.

User needs

Here are a few scenarios, by no means an exhaustive list of the variations and types of disabilities and needs:

  • Someone who cannot hear well will want a visual representation of information presented via sound.

  • Someone who cannot see well will want to hear or feel (via braille or tactile graphics) an equivalent of the visual information.

  • Someone who does not have the strength to move quickly or easily will want to use as little movement as possible and have as much time as they need when operating Web interfaces.

  • Someone who does not read well may want to hear the information read aloud.

If Web content employs the design principles described in this document, then users should be able to access the content using adaptive strategies and assistive technologies. There are many tools that people with disabilities employ to make use of Web content. For more in-depth scenarios of people with disabilities using accessible and inaccessible Web content, please read "How People with Disabilities Use the Web".

Designing Accessible Web Content

These guidelines provide the basic requirements for designing accessible Web content. This document is not designed to provide the background needed to learn about accessible Web design in a thorough or effective manner for those interested in learning. Readers are therefore referred to the Education and Outreach Working Group of the Web Accessibility Initiative.

Principle 1: Content must be perceivable.

Guideline 1.1 Provide text alternatives for all non-text content.

Level 1 Success Criteria for Guideline 1.1

  1. For all non-text content that is functional, such as graphical links or buttons, text alternatives serve the same purpose as the non-text content. [I]

    How to provide text alternatives for content that is functional. (Informative)

  2. For all non-text content that is used to convey information, text alternatives convey the same information. [I]


    for multimedia, this means that two alternatives are provided:

    1. a transcript

    2. a text alternative that identifies the purpose or function of the multimedia

    How to provide text alternatives for content that conveys information. (Informative)

  3. For non-text content that is intended to create a specific sensory experience, such as music or visual art, text alternatives identify and describe the non-text content. [I]

    How to provide text alternatives for content that creates a specific sensory experience. (Informative)

  4. Non-text content that does not provide information, functionality, or sensory experience is marked such that it can be ignored by assistive technology. [I]

    How to provide text alternatives that can be ignored by assistive technology. (Informative)

  5. Any text alternatives are explicitly associated with the non-text content. [I]

    How to explicitly associate text alternatives with non-text content. (Informative)

  6. For live audio-only or live video-only content, such as internet radio or Web cameras, text alternatives describe the purpose of the presentation or a link is provided to alternative real-time content, such as traffic reports for a traffic Web camera

    Note: real-time content does not imply real-time captions.

    Editorial Note: This is similar to #1 above, yet it seems we need to specifically address audio-only and video-only content to avoid confusion.

Level 2 Success Criteria for Guideline 1.1

  1. No level 2 success criteria for this guideline.

Level 3 Success Criteria for Guideline 1.1

  1. For multimedia content, a combined transcript of audio descriptions of video and captions is provided. [I]

    How to provide descriptions of all important visual information for multimedia. (Informative)

Guideline 1.1 (text-equiv) Issues

Who Benefits from Guideline 1.1 (Informative)

  • People who are blind, have low vision, have cognitive disabilities or have trouble reading text for any reason can have the text read aloud to them by assistive technology or otherwise transform the presentation of the text to meet their needs (e.g., change the font face, the text size, or the background and foreground colors).

  • People who are deaf, are hard of hearing, or who are having trouble understanding audio information for any reason can read the text presentation or have it translated and presented as sign language by assistive technology.

  • People who are deaf-blind can read the text in braille.

  • Additionally, text alternatives support the ability to search for non-text content and to repurpose content in a variety of ways.

Examples of Guideline 1.1 (Informative)

  • Example 1: an image used as a button.

    A magnifying glass icon is used to link to the search page of a Web site. A screen reader identifies the button as a link and speaks the text alternative, "Search."

  • Example 2: a data chart.

    A bar chart compares how many widgets were sold in June, July, and August. The short label says, "Figure one - Sales in June, July and August." The longer description identifies the type of chart, provides a high-level summary of the data comparable to that available from the chart, and provides the data in a table.

  • Example 3: an audio recording of a speech (no video).

    The link to an audio clip says, "Chairman's speech to the assembly." A link to a text transcript is provided immediately after the link to the audio clip.

  • Example 4: a recording of a symphony.

    The link to an audio file says, "Beethoven's 5th Symphony performed by the Vienna Philharmonic Orchestra."

  • Example 5: an animation that illustrates how a car engine works.

    An animation shows how a car engine works. There is no audio and the animation is part of a tutorial that describes how an engine works. All that is needed is a description of the image. From "How car engines work: Internal combustion"

  • Example 6: a pair of images used to create a visual effect.

    Two images are used to create curved edges on a "tab" interface. The images do not provide information, functionality, or a sensory experience and are marked such that they can be ignored by an assistive technology.

  • Example 7: an internet radio station.

    A radio station broadcasts over the internet. The station's Web site describes the type of music played, a schedule of the shows, and the "current song" is updated each time the DJ starts a new track. Interviews are recorded and published in the archives. Transcripts of the archived interviews are provided per Guideline 1.2 Provide synchronized alternatives for multimedia.

    Editorial Note: Does the above example help to clarify level 1 success criterion 6 or does it need additional clarification?

  • Example 8: a traffic Web camera.

    A Web site allows end-users to select from a variety of Web cameras positioned throughout a major city. After a camera is selected, the image updates every 2 minutes. A short text alternative identifies the Web camera as, "TraffiCam." The site also provides a table of travel times for each of the routes covered by the Web cameras. The table is also updated every 2 minutes.

Guideline 1.2 Provide synchronized alternatives for multimedia.

Level 1 Success Criteria for Guideline 1.2

  1. Captions are provided for prerecorded multimedia. [I]
  2. Audio descriptions of video are provided for prerecorded multimedia [I]

    Editorial Note: Even though there are instances where captions and audio descriptions of video are not required, this version of Guideline 1.2 does not attempt to address the variations. Instead, it assumes more detail is included in the techniques documents and that policy makers will clarify when captions and audio descriptions of video are required.

  3. If multimedia content is rebroadcast from another medium, the accessibility features required by policy for that medium are intact.

Editorial Note: How should we address presentations that contain only audio or only video and require users to respond interactively at specific times during the presentation? Since it is not multimedia, a criterion could be added to guideline 1.1. However, the need is for synchronized alternatives, therefore a criterion could be added to this guideline. Refer to Issue 1272.

Level 2 Success Criteria for Guideline 1.2

  1. Real-time captions are provided for live multimedia. [I]

Level 3 Success Criteria for Guideline 1.2

  1. Sign language interpretation is provided for multimedia

  2. Extended audio descriptions of video are provided for prerecorded multimedia.

  3. Audio descriptions of video are provided for live multimedia.

Guideline 1.2 (media-equiv) Issues

Who Benefits from Guideline 1.2 (Informative)

  • People who are deaf or have a hearing loss can access the auditory information through captions.

  • People who are blind or have low vision as well as those with cognitive disabilities who have difficulty interpreting visually what is happening benefit from audio descriptions of visual information.

People without disabilities also benefit from media alternatives:

  • People in noisy environments or with muted sound often rely on captions.

  • Captions help many people to develop language and reading skills.

  • Audio descriptions provide visual information for people who are temporarily looking away from the video presentation, for example, when following an instructional video and looking at their hands.

  • Captions and text descriptions make it possible to index and search media files.

Examples of Guideline 1.2 (Informative)

  • Example 1: a movie with audio description.

    Transcript of audio based on the first few minutes of, "Teaching Evolution Case Studies, Bonnie Chen" (copyright WGBH and Clear Blue Sky Productions, Inc.)

    Describer: A title, "Teaching Evolution Case Studies. Bonnie Chen." Now, a teacher shows photographs.

    Bonnie Chen: These are all shot at either the Everglades...for today you just happen to be a species of wading bird that has a beak like this."

    Describer: She hands them each two flat, thin wooden blades

  • Example 2: a captioned tutorial.

    A video clip shows how to tie a knot. The captions read, "(music)




    From Sample Transcript Formatting by Whit Anderson

  • Editorial Note: Examples to be developed: an animation with soundtrack of music with lyrics, an interactive slideshow, an animation with musical soundtrack..

Guideline 1.3 Ensure that information, functionality, and structure are separable from presentation.

Level 1 Success Criteria for Guideline 1.3

  1. Structures within the content can be programmatically determined. [I]

    How to ensure that structures and relationships in content can be programmatically determined. (Informative)

    Editorial Note: The concepts of "reliable" and "standard" need to be incorporated into the definition of "programmatically."

  2. Emphasis can be programmatically determined. [I]

    How to ensure that emphasis can be programmatically determined. (Informative)

  3. Any information conveyed through color can be programmatically determined. For example, through markup or unique characters that accompany the color coding. [I]

    How to make information presented in color available through context or markup. (Informative)

Level 2 Success Criteria for Guideline 1.3

  1. Any information that is conveyed through color is visually evident without having to interpret color. For example, the distinction can additionally be determined through context, characters, or symbols that accompany the color presentation, or through pattern differences such as dotted red vs. solid green lines in a graph. [V]

    How to make information presented in color available without having to interpret markup. (Informative)

Level 3 Success Criteria for Guideline 1.3

  1. No level 3 success criteria for this guideline.

Guideline 1.3 (content-structure-separation) Issues

Who Benefits from Guideline 1.3 (Informative)

  • Separating content and structure from presentation allows Web content to be presented differently to meet the needs and constraints of different users without losing any of the information or structure. For example, information can be presented via speech or braille (text) that was originally intended to be presented visually.

  • It can also facilitate automatic emphasis of structure or more efficient navigation.

  • All of these can benefit people with cognitive, physical, hearing, and visual disabilities.

Examples of Guideline 1.3 (Informative)

Editorial Note: These examples are improvements on previous drafts, but are HTML-specific. These will be generalized in future drafts.

  • Example 1: A form that mentions in text which required fields are missing.

    When a user submits a form without filling in all the required fields, a message appears that informs the user which fields are missing. The missing fields are also indicated in color to help people with cognitive limitations recognize what fields need attention. Because the message is also available in text, people who cannot see color well will still know which fields they have to correct.

  • Example 2: A bus schedule where the headers have been associated with the cells.

    A bus schedule consists of a table with the bus stops listed vertically and the different trips listed horizontally. Each cell contains the time when that bus will be at that bus stop. Structural markup has been used to associate that cell with both the corresponding bus stop and the corresponding trip.

  • Example 3: A form where the labels for the checkboxes have been associated with the checkboxes.

    In a form where users can select different options using checkboxes, the labels for the checkboxes have been associated with the checkboxes. This benefits different types of users. It allows users who are blind to determine what the checkbox is for. People with limited motor functions can check the checkbox more easily because they can click anywhere on the label instead of just on the checkbox.

Guideline 1.4 Make it easy to distinguish foreground information from background images or sounds.

Level 1 Success Criteria for Guideline 1.4

  1. Any text that is presented over a background image, color, or text can be programmatically determined. [I]


Images of text that meets guideline 1.1 should satisfy this criterion. (Refer to Guideline 1.1 Provide text alternatives for all non-text content. )

Level 2 Success Criteria for Guideline 1.4

  1. Text and diagrams that are presented over a background image, color, or text have a contrast greater than X1 where the whiter element is at least Y1 as measured by _____. [V]
  2. Text that is presented over a background pattern of lines which are within 500% +/- of the stem width of the characters or their serifs must have a contrast between the characters and the lines that is greater than X2, where the whiter element is at least Y2. [V]
  3. Users can disable background audio that plays automatically on a page so that it does not interfere with text reading software they may be using. [V]

Editorial Note: The working group is seeking an algorithm that measures contrast in a way that is accurate and testable enough that we could include it in the guidelines. One algorithm, which comes from the Techniques For Accessibility Evaluation And Repair Tools document, is currently under consideration for inclusion in the techniques, but the group has not yet found something that is specific enough to be included at the guidelines level.

Level 3 Success Criteria for Guideline 1.4

  1. Text is not presented over any background (image, text, color or pattern), or if any background is present, the contrast between the text and the background is greater than X2. [V]
  2. Audio content does not contain background sounds or the background sounds are at least 20 decibels lower than the foreground audio content, with the exception of occasional sound effects. [V]


A 20 decibel difference in sound level is roughly 4 times quieter (or louder). Background sound that meets this requirement will be approximately four times (4x) quieter than the foreground audio content.

Guideline 1.4 (visual-audio-contrast) Issues

Who Benefits from Guideline 1.4 (Informative)

  • Individuals with low vision can easily read characters in the content even if they don't have the wide field of view or full range of color perception used by fully sighted persons to separate text from background images. This will also aid comprehension for individuals with cognitive disabilities who benefit from easy discernment of text. Visual contrast also helps individuals with hearing impairments who are aided by clear visual representation of information

  • Individuals with hearing impairments that limit their ability to hear all of the frequencies of speech can make out the words from the sounds they can hear because they are not mixed with residual sounds from music or other background sounds.


Audio contrast is also known as "signal to noise ratio" by audiologists, where "signal" refers to the foreground and "noise" refers to the background.

Examples of Guideline 1.4 (Informative)

  • Example 1: a background image on a page.

    A background image and text are arranged so that there is no image behind the text or the image is so faint that the difference between the darkest part of the image and the text (which is dark) meets the standard foreground/background contrast requirements. The image behind the text also does not contain lines that are about the same width as the characters so they do not interfere with character recognition. This example could also apply to light letters on a dark background.

  • Example 2: speech over background sounds.

    Because speech is often naturally mixed with background sounds (movies, live news etc) and cannot be easily removed or separated, captions are provided (under guideline 1.2) to make dialog understandable. However not all people can see or read the captions. Where speech is mixed or recorded so that it is at least 20 db above any background sounds, most people do not need to rely on captions to understand the dialog.

Principle 2: Interface elements in the content must be operable.

Guideline 2.1 Make all functionality operable via a keyboard or a keyboard interface.

Level 1 Success Criteria for Guideline 2.1

  1. All of the functionality of the content, where the functionality or its outcome can be described in a sentence, is operable through a keyboard or keyboard interface. [I]


    This includes author-provided accessibility features.


    Other interfaces (such as a mouse) can be provided in addition to keyboard operation.


    Refer to guideline 4.2 for information regarding user agent support.

Level 2 Success Criteria for Guideline 2.1

  1. Wherever a choice between input device event handlers is available and supported, the more abstract event is used. [I]

Level 3 Success Criteria for Guideline 2.1

  1. All functionality of the content is designed to be operated through a keyboard or keyboard interface.

Guideline 2.1 (keyboard-operation) Issues

Who Benefits from Guideline 2.1 (Informative)

  • Individuals who are blind (and cannot use pointing devices) can have access to the functionality of the Web content or site.

  • Individuals with severe physical disabilities can use speech input (which simulates keystrokes) to both enter data and operate the interface elements on the page.

Examples of Guideline 2.1 (Informative)

  • Example 1: operation with multiple input devices.

    The content relies only on focus-in, focus-out, and activation events; these are defined in the API of the environment for which the content is written, and are intended to be operable by a variety of input devices, including pointing devices, keyboards and speech input systems.

  • Example 2: examples of Web content that would and would not be operable from a keyboard or keyboard interface

    • If it's written to be operable from a computer keyboard, it conforms (because it is operable from the keyboard.)

    • If it's written to be used on a device that doesn't usually have a keyboard such as a cell phone, but it can be controlled by an optional keyboard for that device, it conforms. (A person who needs a keyboard - or alternate keyboard - can use it to control the application.)

    • If it's written to be used with a device that doesn't have a keyboard, but it could also be used by similar devices that do and it would work with their keyboard, it conforms. (A person who needs a keyboard would not buy the device without the keyboard. That device may itself not be considered accessible. But the content can be controlled from a device with a keyboard and therefore conforms to this guideline.)

    • If it's written to work with devices that do not have keyboards and it can not be used by any other devices that do have keyboards, then it does not conform. (It cannot be accessed via keyboard.)

Guideline 2.2 Allow users to control time limits on their reading or interaction.

Level 1 Success Criteria for Guideline 2.2

  1. Content is designed so that time-outs are not an essential part of interaction, or at least one of the following is true for each time-out that is a function of the content: [I]
    • the user is allowed to deactivate the time-out or;

    • the user is allowed to adjust the time-out over a wide range which is at least ten times the length of the default setting or;

    • the user is warned before time expires, allowed to extend the time-out with a simple action (for example, "hit any key") and given at least 20 seconds to respond or;

    • the time-out is an important part of a real-time event (for example, an auction), and no alternative to the time-out is possible or;

    • the time-out is part of an activity where timing is essential (for example, competitive gaming or time-based testing) and time limits can not be extended further without invalidating the activity.

Level 2 Success Criteria for Guideline 2.2

  1. A method is provided to stop content that blinks for more than 3 seconds. [I]
  2. Moving or time-based content can be paused by the user. [I]

Level 3 Success Criteria for Guideline 2.2

  1. Except for real-time events, timing is not an essential part of the event or activity presented by the content. [V]
  2. Non-emergency interruptions, such as the availability of updated content, can be postponed or suppressed by the user. [V]

Guideline 2.2 (time-limits) Issues

Who Benefits from Guideline 2.2 (Informative)

  • People with reading disabilities, cognitive disabilities, and learning disabilities who may need more time to read and comprehend written text can have additional time to read the information.

  • People with physical disabilities can access content that is updated often.

Examples of Guideline 2.2 (Informative)

  • Examples of content that must meet the success criteria of this checkpoint:

    • automatic refresh,

    • redirection,

    • blinking or scrolling text,

    • dialog that disappears after a short period,

    • shutdown or deactivation of resource if activity is not received in a set amount of time.

  • Example 1: blinking text.

    Client-side scripting is used to create blinking text. The content provides an option that allows the user to turn off the blinking.

  • Example 2: a news site that is updated regularly.

    A news site causes its front page to be updated every half hour. The front page contains minimal text and primarily consists of links to content. A user who does not wish the page to update selects a checkbox. The checkbox is in the "user preferences" portion of the site which is one of the first links on each page.

Guideline 2.3 Allow users to avoid content that could cause seizures due to photosensitivity.

Level 1 Success Criteria for Guideline 2.3

  1. Content that violates international health and safety standards for general flash or red flash is marked in a way that the user can avoid its appearance. [V]

Level 2 Success Criteria for Guideline 2.3

  1. Content does not violate international health and safety standards for general flash or red flash. [V]

Level 3 Success Criteria for Guideline 2.3

  1. Content does not violate international health and safety standards for spatial pattern thresholds or red flash. [V]

Editorial Note: A free tool will be available from the University of Wisconsin's Trace Center that will carry out the above analysis on Web content.

Guideline 2.3 (flicker) Issues

Who Benefits from Guideline 2.3 (Informative)

  • Individuals with photosensitive epilepsy can avoid having seizures triggered by flashing or by spatial patterns.

Guideline 2.4 Provide mechanisms to help users find content, orient themselves within it, and navigate through it.

Level 1 Success Criteria for Guideline 2.4

  1. Structures and relationships within the content can be programmatically determined. [I]


    Conforming to the first level 1 criterion in Guideline 1.3 Ensure that information, functionality, and structure are separable from presentation. also addresses this guideline at level 1.

    Editorial Note: The working group seeks input about the overlap of criterion for guidelines 1.3 and 2.4.

Level 2 Success Criteria for Guideline 2.4

  1. Documents that have five or more section headings and are presented as a single delivery unit include a table of contents with links to important sections of the document. [V]

    How to provide a table of contents with links to important sections. (Informative)

  2. There is more than one way to locate the content of each delivery unit, including but not limited to link groups, a site map, site search or other navigation mechanism. [V]

    How to provide more than one way to locate the content of each delivery unit. (Informative)

  3. Blocks of repeated material, such as navigation menus and document headers, are marked up so that they can be bypassed by people who use assistive technology or who navigate via keyboard or keyboard interface. [V]

    How to mark blocks of repeated material so they can be bypassed. (Informative)

    Editorial Note: General Techniques might include something about satisfying this criterion through metadata, use of a future role attribute, etc.

Level 3 Success Criteria for Guideline 2.4

  1. When content is arranged in a sequence that affects its meaning, that sequence can be determined programmatically. [I]

    How to ensure that reading sequence can be determined programmatically. (Informative)

    Editorial Note: The problem is how to specify that this criterion applies to content that is intended to appear as a sequence without requiring a test for intention. It has been suggested that reading order is already covered by the requirement in 1.3 to make structures and relationships within the content programmatically determinable. If the Working Group and other readers share this view, this could be deleted as a separate SC and the accompanying General Technique could be moved to guideline 1.3.

    Editorial Note: The criterion about reading order may be more appropriate under Principle 3: it could be argued that reading order is irrelevant unless it affects the user's ability to understand the content. Reading order in itself is not necessarily an accessibility issue. It becomes an accessibility issue if a user with a disability (such as a visual or cognitive impairment) could not reliably derive a meaningful reading order from the default presentation. If we want to retain this criterion and keep it under 2.4, we need to craft wording that ties reading order to users' ability to operate and use the content. It is not necessarily true that merely exposing structure to the user agent is sufficient to indicate a plausible reading order. The example for the General Technique about reading order is designed to highlight this issue.

  2. When a page or other delivery unit is navigated sequentially, elements receive focus in an order that follows relationships and sequences in the content. [I]

    How to ensure that elements receive focus in an order that follows relationships and sequences in the content. (Informative)

  3. Images have structure that users can access. [I]

    How to provide structure for images. (Informative)

  4. Delivery units have descriptive titles [I]

    How to provide descriptive titles. (Informative)

  5. Text is divided into paragraphs. [V]
  6. Documents are divided into hierarchical sections and subsections that have descriptive titles. [V]

Guideline 2.4 (navigation-mechanisms) Issues

Who Benefits from Guideline 2.4 (Informative)

  • When the logical structure is provided in markup or a data model,

    • Users with physical disabilities can use structure to more easily jump between paragraphs, chapters, sections etc.

    • Users with cognitive disabilities can use structure (chapter titles, headers, etc.) to provide more context for the text that follows them. They also provide warning of a change in context and reorient the user to the new focus.

    • Users with blindness or low vision can jump from header to header to get an overview or to more quickly "skim" to the section they are interested in.

    • Readers with low vision can sometimes (depending on display technology) change how chapter titles and headers are displayed to make them more visible and easier to use when skimming the document.

    • the content can be presented on a variety of devices because the device software can choose only those elements of the content that it is able to display and display them in the most effective way for that device.

  • Providing different navigation mechanisms can provide a better match between different people's skills, background knowledge, visual vs. text orientation, and the type of information they are seeking at the moment.

  • Individuals with cognitive disabilities may find it easier to ask for what they want than to deduce its location from categorical choices.

  • Individuals with low vision or blindness may find search techniques that fetch everything that relates to a topic of interest to be easier than techniques that require them to scan lists or content for the items.

  • Presentation that emphasizes structure:

    • enables users with cognitive and visual disabilities to orient themselves within the content,

    • enables all users to move quickly through the content and notice major content divisions

    • enables all users, but particularly users with visual or cognitive disabilities to focus on important content,

    • enables all users, but particularly users with visual or cognitive disabilities to distinguish the different types of content.

Examples of Guideline 2.4 (Informative)

  • Example 1: documentation for a product.

    Identifying chapters in the structure of a book is appropriate and accepted way of labeling the structure. Within the chapters, headings identify (label) changes in context and highlight ideas contained in the following text. Subtle differences between the appearance of the chapter title and the section headings helps the user understand the hierarchy and relationship between the title and headings. The difference might be font size and margin indentation when presented visually, and spoken in a different voice or preceded by a sound when presented auditorily.

  • Example 2: a scalable image of a bicycle.

    Lines and a circle (spokes and rim) are grouped into a "wheel." Lines in a triangle that attach to each wheel are grouped into a "frame."

  • Example 3: user interface.

    User interface controls are divided into organized groups.

  • Example 4: a data table.

    Groups of rows or columns are labeled with headers.

  • Example 5: an audio presentation.

    An audio rendering of a document, generated according to a style sheet, uses a different, more formal voice to read titles and headers so the listener can easily identify the words as a title and not part of the running text.

Guideline 2.5 Help users avoid mistakes and make it easy to correct them. [level 2 guideline]

Level 1 Success Criteria for Guideline 2.5

  1. No level 1 success criteria for this guideline.

Level 2 Success Criteria for Guideline 2.5

  1. If an input error is detected, the error is identified and provided to the user in text.

  2. If an input error is detected and suggestions for correction are known and can be provided without jeopardizing the security or purpose of the content, the error is identified and the suggestions are provided to the user.

  3. For forms that cause legal or financial transactions to occur, that modify or delete data in remote data storage systems, or that submit test responses, at least one of the following is true:

    1. Actions are reversible.

    2. Where not reversible, actions are checked for errors before going on to the next step in the process.

    3. Where not reversible, and not checkable, the user is able to review and confirm or correct information before submitting it.

Level 3 Success Criteria for Guideline 2.5

  1. Where text entry is required for which there is a known set of less than 75 valid choices and they can be provided without jeopardizing security or purpose, users are allowed to select from a list of options as well as to type the data directly.

  2. If possible for the natural language of the text, an option is provided to check text entries for misspelled words with suggestions for correct spellings.

Guideline 2.5 (minimize-error) Issues

Who Benefits from Guideline 2.5 (Informative)

  • Identifying typing errors helps individuals with writing disabilities and people with dyslexia who often have difficulty writing text in forms or other places that need text input.

  • Certain disabilities make it more difficult to operate input devices, resulting in more input errors. For example, individuals with limited motor functions are more likely to make errors when they operate a mouse or a keyboard. Speech recognition systems may find it more difficult to recognize the speech of individuals with speech disabilities. Features that assist in recognizing and correcting errors benefit individuals with these types of disabilities.

Examples of Guideline 2.5 (Informative)

  • Example 1: Identifying errors in a form submission.

    An airline web site offers a special promotion on discounted flights. The user is asked to complete a simple form that asks for personal information such as name, address, phone number, seating preference and e-mail address. If any of the fields of the form are either not completed or completed incorrectly, the user is warned of the input error. The user is then presented with the same form, all previously and correctly entered information is still available. The user is asked to make corrections to any form field marked with a red arrow or two asterisks. Note: color alone is not used to indicate errors.

  • Example 2: Username and password errors.

    A Web page requires the user to enter both a username and password. If either is incorrect, the user is informed that there was an error but, for security reasons, is not informed as to which field, the username or the password, is in error and suggestions for correcting are not offered.

  • Example 3: An online test.

    A Web site provides an online test for certification in a particular field of study. The test identifies incorrect answers to the user but does not offer suggestions for correcting them. The purpose of the online test is to test the user's knowledge, therefore, providing hints on correct answers would go against the purpose of the Web site.

  • Example 4: Order confirmation.

    A Web retailer offers online shopping for customers. When an order is submitted, the order information, including items ordered, quantity of each ordered, shipping address, and payment method, are displayed allowing the user to inspect the order for correctness. The user can either confirm the order or make changes.

  • Example 5: A selection list to reduce errors.

    A Web retailer offers online shopping for customers interested in fly fishing gear. When the user is asked for his/her country, a pulldown list of countries is offered instead of having the user enter the information by typing. To possibly make things easier, the user is informed that countries are listed in alphabetical order.

  • Example 6: Search engine features.

    A search engine is provided with a variety of search options for different skill levels and preferences. It includes an option to check the spelling of the search terms and offers "best guess" alternatives, query-by-example searches, and similarity searches.

  • Example 7: Spell checking in feedback forms.

    A banking Web site provides a form for customers to submit questions or suggestions. The form user interface includes an optional spell-checking feature for the text input area where the question or suggestion is entered.

  • Example 8: Expected date format in a form.

    In a form, there is a text box for "birthday". Next to this text box is the text "(MM-DD-YYYY)" to indicate the format in which the date should be entered.

Principle 3: Content and controls must be understandable.

Guideline 3.1 Ensure that the meaning of content can be determined.

Level 1 Success Criteria for Guideline 3.1

  1. The primary natural language or languages of the delivery unit can be programmatically determined. [I]
  2. The meaning of abbreviations and acronyms can be programmatically located. [I]

Level 2 Success Criteria for Guideline 3.1

  1. The meanings and pronunciations of all words in the content can be programmatically located. [I]
  2. For each foreign language passage or phrase in the body of the content, the language is identified through markup or other means. Foreign passages or phrases are passages or phrases that are in a language other than the primary language of the document. [I]


    This does not include use of foreign words in text where such usage is a standard extension of the language.

Level 3 Success Criteria for Guideline 3.1

  1. A mechanism is available for identifying specific definitions of words used in an unusual or restricted way, including idioms and jargon. [I]

    Editorial Note: We need to define tests for "unusual or restricted way."

  2. Where a word has multiple meanings and the intended meaning is not the first in the associated dictionary(s), then additional markup or another mechanism is provided for determining the correct meaning. [I]
  3. Section headings and link text are understandable when read by themselves or as a group (for example, in a screen reader's list of links or a table of contents). [V]
  4. There is a statement associated with the content asserting that the Strategies for Reducing the Complexity of Content (the following list) were considered. [V]

    Editorial Note: We are still examining methods to make some or all of these testable (which might make them success criteria on their own).

    • In general

      • Organizing material so it is easy to read and use.

      • Using a style manual, dictionary, and other reference materials.

      • Testing documents to learn if potential users understand the material, and including people with cognitive, learning, or reading disabilities in the test group.

      • Developing a single topic or subtopic per paragraph.

    • Vocabulary

      • Using vocabulary that is likely to be familiar to intended readers.

        • If the resource is intended for people who work in a particular technical field, consider using a Controlled Language. For example, a resource designed for aircraft engineers could use a controlled language like the one used by Boeing Aircraft Company.

        • If a technical resource is intended for translation into other languages, consider using a Controlled Language.

        • Avoiding professional jargon, slang, and other terms with a specialized meaning that may not be clear to people outside a specific group when resources are intended for a general audience or for translation into other languages,. It may also be helpful to review the document for plain language, using a checklist like the ones produced by US and Canadian government agencies.

        Editorial Note: Need to add examples from other countries and other languages.

      • Using length and complexity of sentences that are consistent with recommended best practices for the intended audience, such as those found in current textbooks about writing in the audience's field or discipline.

    • Sentences

      • Making sentence-length consistent with common practice in the language of the document or the primary audience for whom the document is intended. Textbooks about writing in that field or related disciplines may be useful when such textbooks are available.

    • Syntax

      • Using the simplest sentence forms consistent with the purpose of the content

        • For example, the simplest sentence-form for English consists of Subject-Verb-Object, as in John hit the ball or The Web site conforms to WCAG 2.0.

      • Using bulleted or numbered lists instead of paragraphs that contain long series of words or phrases separated by commas.

    • Nouns, noun-phrases, and pronouns

      • Using single nouns or short noun-phrases.

      • Making clear pronoun references and references to earlier points in the document

        Example of potential ambiguity: The sentence below contains several pronouns whose references are not clear:

        Web developers can't understand those guidelines because they don't speak their language.

        1. It is not clear which guidelines are referred to as "those guidelines" (the guidelines you are reading now would be these guidelines)

        2. It isn't clear whether the pronoun "they" refers to the Web developers or to the guidelines (the rules of English syntax indicate that the reference is to the guidelines, but common usage doesn't always obey those rules)

        3. It isn't clear whether the pronoun "their" refers to the language used by the Web developers or the language in which the guidelines are written.

        The sentence can be rewritten to resolve the ambiguities:

        Web developers can't understand these guidelines because the guidelines are not written in the developers' language.

    • Verbs

    • Voice

      • Using the active voice for documents written in English and some other Western languages, unless there is a specific reason for using passive constructions. Sentences in the active voice are often shorter and easier to understand than those in the passive voice.

        • Active: Many people believe that readers understand sentences in the active voice more easily than sentences in the passive voice.

        • Passive: It is believed by many that sentences in the active voice are more easily understood by readers than sentences in the passive voice.

    • Tenses

      • Using verb tenses consistently.

        For example, do not switch randomly between past and present tense. In the sentences, John left the room. He takes the elevator down to the lobby, the shift from past tense (in the first sentence left the room) to present tense in the second sentence (takes the elevator) might create ambiguity about John's use of the elevator: did he use it in the past or is he using it now?

    • Logic and relationships

      • Indicating logical relationships between phrases, sentences, paragraphs, or sections of the text.

        • In some cases, simple words such as and, however, furthermore, and therefore may be enough to make the logical relationship clear between one sentence and the next. Other cases may require longer phrases or even additional sentences.

    • Instructions and operable content

      • Thoroughly explaining instructions or required actions.

      • Using names and labels consistently.

      • Being clear where the document:

        • explains choices and options,

        • labels options to get more information,

        • instructs users how to modify selections in critical functions (such as how to delete an item from a shopping cart).

      • Using a goal-action structure for menu prompts.

      • Using default settings (and the ease in re-establishing them)

      • Using two-step, "select and confirm" processes to reduce accidental selections for critical functions

      • Providing calculation assistance to reduce the need to calculate (for example, use a script to calculate the total price for an online purchase)

    • Alternative representations: summaries, paraphrases, examples, illustrations, and symbolic languages

      • Providing summaries to aid understanding.

      • Adding non-text content to the site for key pages or sections specifically to make the site more understandable by users who cannot understand the text only version of the site.

        Editorial Note: WCAG 1.0 and Section 508 both allow text-only variants only in cases when the "original" can't be made accessible any other way, and then require that the text-only variant be updated whenever the "original" changes. That seems to have dropped out of WCAG 2.0, but we think we need to reinstate it.

      • Using page design, graphics, color, fonts, animations, video, or audio to clarify complex text.

      • Including non-text content to supplement text for key pages or sections of the site.

Guideline 3.1 (meaning) Issues

Who Benefits from Guideline 3.1 (Informative)

  • Phrases from various languages are often interspersed in writing. When these phrases are identified, a speech synthesizer can voice text with the appropriate accent and pronunciation. When they are not identified, the speech synthesizer will use the default accent and pronunciation of the language on the rest of the content, which can make the phrase unintelligible. Identifying changes in language will also allow a tool to ask for automatic translations of that content. When editing content, authoring tools can switch between appropriate spelling dictionaries.

  • Providing the expansion of abbreviations and acronyms not only helps people who are not familiar with the abbreviation or acronym but can clarify which meaning of an abbreviation or acronym is appropriate to use. For example, the acronym "ADA" stands for both the American with Disabilities Act as well as the American Dental Association.

  • Defining key terms and specialized language will help people who are not familiar with the topic.

  • Facilitating unambiguous decoding of characters and words in content is also helpful for individuals who are learning to read or learning a second language.

  • All users, especially those with cognitive, learning, and/or reading disabilities benefit from the use of clear and simple writing. This should not discourage you from expressing complex or technical ideas.

  • Using clear and simple language also benefits people whose first language differs from your own, including those people who communicate primarily in sign language.

  • Sounds, graphics, videos and animations can help make concepts presented in a Web site easier to understand, especially for people with cognitive, reading, or learning disabilities or those who are unfamiliar with the language of the text of the site.

  • Summarizing information that is difficult to understand helps people who do not read well.

  • Providing a summary of the visual cues that show relationships between complex information helps people who do not use visual cues or who have difficulty using visual cues. For example, people who are completely blind do not use any visual cues, while people with dyslexia or with low vision might have difficulty interpreting visual cues.


Designers need to be cautious in deciding when to use illustrations. Reading a picture is probably a learned activity that is easier for some than others. Some users skip the pictures; others read only the pictures. Designers must also recognize that visual conventions are not universal and that individuals develop their own mental schema and expectations in interpreting visual information.

Examples of Guideline 3.1 (Informative)

  • Example 1: an acronym in a page title.

    In the following heading, "People of the W3C." the acronym "W3C" is marked as an acronym. Because it has been marked appropriately, the user agent would be able to speak the letters of the acronym one at a time rather than attempting to pronounce it as though it were a word.

  • Example 2: a French phrase in an English sentence.

    In the following sentence, "And with a certain je ne sais quoi, she entered both the room, and his life, forever." the French phrase "je ne sais quoi" is marked as French. Depending on the markup language, English may either be marked as the language for the entire document except where specified, or marked at the paragraph level.

  • Example 3: a description of a process.

    A page describes how to learn to play soccer. Each step in learning the fundamentals of the game is illustrated with a photograph of a player doing what is described in the text.

  • Example 4: a description of a complex natural event.

    A Web page discusses Mt. Pinatubo in the Phillipines. The page includes a description of the 1991 eruption as well as photos of the eruption and its aftermath. The page also includes a brief explanation of why volcanoes erupt. To clarify this explanation, there is also a link to an accessible video and 3D simulation of what happened underneath the crust and within the volcano during the eruption.

  • Example 6: stock trading data.

    A news site is comparing the performance of the economy from 3rd quarter of this year with 3rd quarter from the last 3 years. They compare prices of the most popular stocks. They present the data in a bar graph with a link to the raw data they used to create the bar graph.

  • Example 7: history of music.

    A grandfather's hobby is listening to and playing music. He creates a Web site that includes examples of many different types of music and musical instruments. When describing specific types of music, he links to a short sound clip.

Guideline 3.2 Organize content consistently from "page to page" and make interactive components behave in predictable ways.

Editorial Note: We are looking for a word to replace "page" that applies across technologies. For visual applications, "screen" would apply, but would not apply for speech-based technologies such as VoiceXML.

Level 1 Success Criteria for Guideline 3.2

  1. Any extreme change of context is implemented in a manner that can be programmatically identified. [I]

Level 2 Success Criteria for Guideline 3.2

  1. Components that are repeated on multiple "pages" within a resource or a section of a resource occur in the same sequence each time they are repeated, for at least one presentation format. [V]
  2. All user interface components should be able to receive focus without causing activation. [I]
  3. Changing the setting of any input field should not automatically cause an extreme change in context such as leaving the "page." [V]
  4. Interactive elements that appear on multiple "pages," including graphical elements, are associated with the same functionality wherever they appear. [I]
  5. Explicit notice is given in advance of any extreme change of context. [V]

    Editorial Note: This criterion is HTML-specific.

  6. The destination of each link is identified through words or phrases that either occur in the link or can be programmatically determined. [V]

    Editorial Note: There is some debate about whether this criterion should be this specific. There is also a question as to whether it should be included at level 2 or level 3.

Level 3 Success Criteria for Guideline 3.2

  1. Graphical components that appear on multiple pages, including graphical links, are associated with the same text equivalents wherever they appear. [V]
  2. Components that appear visually on multiple pages, such as navigation bars, search forms, and sections within the main content, are displayed in the same location relative to other content on every page or screen where they appear. [V]
  3. When components such as navigation menus and search forms appear on multiple pages, users can choose to have those elements presented in a different visual position or reading-order. [V]
  4. There are no extreme changes of context. [V]

Editorial Note: There is concern that many of these success criteria are very HTML-specific.

Guideline 3.2 (consistent-behavior) Issues

Who Benefits from Guideline 3.2 (Informative)

  • Providing consistent and predictable responses to user actions is important feedback for users. This lets them know that your site is working properly and encourages them to continue interacting with the content. When users receive an unexpected response, they might conclude that something is wrong or broken. Some people might become so confused they will not be able to use your site.

  • Individuals who are unable to detect extreme changes in context or may not realize that the context has changed are less likely to become disoriented while navigating a site. This applies to people in the following ways:

    • Individuals who are blind or have low vision may have difficulty knowing when a visual context change, such as a new window popping up, has occurred. In this case, warning users of context changes in advance minimizes confusion when the user discovers that the back button no longer behaves as expected.

    • Using captions to note changes in speaker is beneficial for individuals who are deaf or hard of hearing and who may be unable to discern changes in speaker for audio-only presentations.

  • Some individuals with low vision, with dyslexia and who have difficulty interpreting visual cues may benefit from additional cues in order to detect extreme changes in context.

Examples of Guideline 3.2 (Informative)

  • Example 1: a form to deactivate pop-up windows.

    A checkbox is provided on a page of links to let the user select whether they want the resultant pages to appear in new windows or not.

  • Example 2: a warning is given before displaying a pop-up window.

    At the end of a news story, several links are provided for more information. At the beginning of each link is an icon of an arrow with the text equivalent, "Link will open in new window."

  • Example 3: frames that do not track history making the back button behave unexpectedly.

  • Example 4: forms.

Editorial Note: These examples need to be completed or replaced with better examples.

Principle 4: Content must be robust enough to work with current and future technologies.

Guideline 4.1 Use technologies according to specification.

Level 1 Success Criteria for Guideline 4.1

  1. Except where the site has documented that a specification was violated for backward compatibility or compatibility with assistive technology, the technology has: [I]
    1. passed validity tests for the version of the technology in use (whether it be conforming to a schema, Document Type Definition (DTD), or other tests described in the specification),

    2. structural elements and attributes are used as defined in the specification.

Level 2 Success Criteria for Guideline 4.1

  1. No level 2 success criteria for this guideline.

Level 3 Success Criteria for Guideline 4.1

  1. Technologies are used according to specification without exception. [V]

Guideline 4.1 (use-spec) Issues

Who Benefits from Guideline 4.1 (Informative)

  • This guideline further emphasizes that following specifications increases the likelihood of accessible content. While other guidelines refer to individual pieces of content, this guideline takes a step back to look at the broad picture. It also exists to help cover future technologies or issues that we did not anticipate at the time of writing this guideline. Thus, the benefits of following specifications are primarily that assistive technologies and user agents can render the content according to specification.

  • Following specifications for markup and other file formats makes it possible to more easily reformat, repurpose and reuse content, which is important to users who can only make full use of content when presented in a particular format.

Examples of Guideline 4.1 (Informative)

  • Example 1: structural elements.

    Throughout a historical Web site, structural elements are used appropriately to indicate the presence of quotations, definitions and bibliographic references. Because these elements have (only) been used according to specification, user agents can be configured so that these elements are differentiated from the rest of the content, allowing an end user to optimize her use of the site for research purposes.

  • Example 2: presentation elements.

    A Web author wishes to focus attention on a series of words on a page for purely artistic reasons. He uses elements devoid of semantic meaning, rather than elements that are designed to convey information about the structure or organization of a page, to enhance the visual presentation and avoids implying unintended meaning about page organization for non-visual or text-only users.

Guideline 4.2 Ensure that user interfaces are accessible or provide an accessible alternative(s)

Level 1 Success Criteria for Guideline 4.2

  1. For any technologies not in the chosen baseline, the following are true:
    1. The Web content still conforms using user agents that only support the technologies that are in the baseline (i.e. the use of technologies that are not in the baseline does not "break" access to the Web content by user agents that don't support them.)

    2. All content and functionality are available using only the baseline technologies.

  2. Any programmatic user interface components of the content conform to at least the default set of conformance requirements of the UAAG 1.0 at Level A plus the sets of requirements (a) through (i) (below) that apply. If the custom user interfaces cannot be made accessible, an alternative solution is provided that meets WCAG 2.0 (including this provision) to the level claimed. [V]

    Requirements (a) through (i)

    1. If the application renders visual text, it should conform to the VisualText checkpoints.

    2. If the application renders images, it should conform to the Image checkpoints.

    3. If the application renders animations, it should conform to the Animation checkpoints.

    4. If the application renders video, it should conform to the Video checkpoints.

    5. If the application renders audio, it should conform to the Audio checkpoints.

    6. If the application performs its own event handling, it should conform to the Events checkpoints.

    7. If the application implements a selection mechanism, it should conform to the Selection checkpoints.

    8. The application should support keyboard access per UAAG 1.0 checkpoints 1.1 and 6.7.

    9. If the application implements voice or pointer input, it should conform to the Input Modality checkpoints.

Level 2 Success Criteria for Guideline 4.2

  1. Accessibility conventions of the markup or programming language (API's or specific markup) are used. [I]

Level 3 Success Criteria for Guideline 4.2

  1. The Web resource includes a list of the technologies user agents must support in order for its content to work as intended. The list is documented in metadata if such metadata is supported by the format, otherwise it is documented in a policy statement associated with the content. [V]
  2. Users who do not have one or more of these technologies can still access and use the resource, though the experience may be degraded. [V]


    When selecting required technologies, consider that assistive hardware and software is often slow to adapt to technological advances, and the availability of assistive technology varies across natural languages. Verify that assistive technology compatible with the technologies you choose is available in the natural language(s) of your content.

  3. Technologies and features on the required list are open standards or have a public specification. [V]

Guideline 4.2 (technology-supports-access) Issues

Who Benefits from Guideline 4.2 (Informative)

  • Authors who ensure the accessibility of user interfaces within their content will:

    • encounter fewer challenges when implementing these guidelines,

    • avoid the need to create custom solutions and workarounds to address accessibility concerns,

    • avoid the need to provide accessible alternate versions for content rendered in a technology that does not fully address these guidelines.

    Benefits of determining and documenting technology requirements:

    • Individuals can identify (either through site documentation or automatically through metadata) whether or not they are likely to be able to use a site. In conjunction with a search engine or a proxy server, this could be used to automatically filter out sites a user can not access or to automatically filter to the top sites that would be most usable.

    • Documenting technology requirements will cause authors to evaluate assumptions about user agents and will minimize the number of sites that are inadvertently inaccessible because they are unaware of backward compatibility issues.

    Benefits of ensuring user interface accessibility and providing accessible alternatives:

    • Individuals who must use alternative browsing technologies and devices will be able to access the content.

    • Individuals who can not afford or otherwise do not have access to newer technologies also benefit from backward compatibility in that they will not need to purchase upgrades or equipment as often.

Examples of Guideline 4.2 (Informative)

  • Example 1: an online store that lists required technologies.

    By documenting minimum user agent requirements, the store makes it possible for people using particular technologies to determine whether they are going to have trouble using the store or its checkout mechanism before they begin shopping. This prevents users from finding that, after they have selected their products and initiated a checkout process, they are unable to complete their transaction. They can, therefore, choose alternatives where they can be assured greater success.

  • Example 2: an intranet site that transforms gracefully.

    A large company was concerned about the ability to address individuals at many diverse office locations that have different technology bases. To address the problem, they created two versions of their content and documented the requirements for each, making it easy for individual locations to determine which version would work best for their technologies.

  • Example 3: an informational site ensuring backward compatibility.

    An information site covers a wide variety of subjects and wants to enable their visitors to quickly find the topics they're looking for. To do this, they have implemented an interactive menu system that is only supported in the most recent version of two popular user agents. To ensure that their visitors who do not use these specific user agents are still able to effectively use the site, a navigation mechanism that does not depend on the interactive menu system they are using is presented to user agents that do not support the newer technology.

  • Example 4: accessible APIs.

    A Java applet uses the accessibility API defined by the language. Refer to the IBM Guidelines for Writing Accessible Applications Using 100% Pure Java.

Appendix A Glossary

Editorial Note: The WCAG WG has not tackled the definitions of the terms that we are using and acknowledges that we sometimes use terms inconsistently. We need to coordinate our terms and definitions with the WAI Glossary and are working on proposals for a variety of definitions. We have been looking at the UAAG 1.0 glossary and other glossaries within the W3C. A list of open issues related to this glossary is available.

activity where timing is essential

An activity where timing is essential is an activity where timing is part of the design of the activity. Removal of the time element would change the performance of the participants. Versions of the activity (e.g. test) that have no time basis or time-outs might be preferred and may be required for some venues but this would require a complete redesign of the activity (e.g. test) and may change the character and validation methodology and would therefore not fall under these guidelines.


Graphic representations that are created by a spatial arrangement of text characters. Although it can be rendered on a text display, it is not text.

audio description

Additional audio narration that explains important details that cannot be understood from the main soundtrack alone. During pauses in dialog, audio descriptions of video provide information about actions, characters, scene changes and on-screen text to people who are blind or visually impaired.

authored unit

Some set of material created as a single entity by an author. Examples include a collection of markup, a style sheet, and a media resource, such as an image or audio clip.


This term was taken verbatim from Glossary of Terms for Device Independence.

background image

Images that appear behind or to the back of the visual field.


Set of technologies assumed to be supported by, and enabled in, user agents in order for Web content to conform to these guidelines.


Some examples of entities that may set baselines that an author may have to follow include the author, a company, a customer and government entities.

Editorial Note: In the techniques document we plan to discuss techniques for conforming to WCAG 2.0 based on three different baselines (i.e. assumptions of technologies supported and active in user agents).


Synchronized transcripts of dialogue and important sound effects. Captions provide access to multimedia for people who are deaf or hard of hearing.

complex content

Content is considered complex if the relationships between pieces of information are not easy to figure out. If the presentation of the information is intended to highlight trends or relationships between concepts, these should be explicitly stated in the summary.

Examples of complex information:

  • data tables,

  • concepts that are esoteric or difficult to understand,

  • content that involves several layers.



Editorial Note: We need to include a definition for content here.

content that blinks

Content that blinks is content that turns on and off between .5 and 4 times per second.

controlled languages

Controlled languages use a restricted vocabulary taken from natural language. The purpose is to make texts easier to understand and translate. Standards generally limit words to a single meaning and prescribed part of speech. Complex syntax is avoided. Information about controlled language applications is available on the World Wide Web.

delivery unit

A set of material transfered between two cooperating web programs as the response to a single HTTP request. The transfer might, for example, be between an origin server and a user agent.


This term was taken verbatim from Glossary of Terms for Device Independence.

event handler

A section of code that responds to an action taken by the user (or user agent). On Web pages, events are usually user actions such as moving the mouse, typing, etc. An event handler determines the response to that action. A technology specific event handler only responds to an action by one kind of input device. An abstract event handler is one which can be activated by a variety of input devices.

explicitly associated

Editorial Note: We need to include a definition of explicit association here.

extended audio description

In cases where a longer audio description is necessary but there is not a sufficient pause in the audio to accommodate it, the audio and video are paused while the audio and description plays. When the description has finished playing, the video and dialog resume playback. Extended and "regular" descriptions may be mixed in a single multimedia presentation.

extreme changes in context

extreme changes in context include:

  • opening a new browser window unexpectedly and without any nonvisual cue (back button suddenly appears nonfunctional)

  • in an auditory presentation, the speaker changes with no visual cue and no notation in captions

  • captions that do not identify a change in speaker

Common user actions include:

  • mouse movements

  • key activation

  • link selection

  • use of browser navigation buttons (e.g. back and forward)

  • opening new browser windows

Common responses to user actions include:

  • loading a new page

  • exposing/concealing content based on mouse position or keyboard focus

  • displaying the contents of a menu (auditorily or visually)

  • displaying pop-up menus or windows

  • submitting a form

It is important that responses to user actions be predictable and sensible to the end user and that interactions are consistent, both throughout the site and with commonly used interaction metaphors used throughout the Web.


A feature is a specific component of a technology, for example an element in a markup language or a function call in an Application Programming Interface. Typically, a given feature may only be available in specific versions of the technology, and thus may need to be noted explicitly in the required list.


Functionality is the purpose or intended effect of the content. This may include presentation of information , data collection, securing a response from the user, providing user experience, linking to other content, testing, confirmation, purchasing, etc.

general flash threshold
  • A sequence of flashes or rapidly changing image sequences is not permitted when both the following occur:

    1. the combined area of flashes occurring concurrently (but not necessarily contiguously) occupies more than one quarter of any 335 x 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels and

    2. there are more than three flashes within any one-second period.


    For the general flash threshold, a flash is defined as a pair of opposing changes in luminance (i.e., an increase in luminance followed by a decrease, or a decrease followed by an increase) of 20 candelas per rectangle meter (cd.m-2) or more and where the screen luminance of the darker image is below 160 cd.m-2.


Thresholds are based on ITC Guidance Note for Licensees on Flashing Images and Regular Patterns in Television (Revised and re-issued July 2001) as modified by the Wisconsin Computer Equivalence Algorithm.

keyboard interface

On devices that do not have a built-in or attached keyboard, there is often an alternate method for connecting a keyboard to the device for the purpose of generating text or an internal method for generating text. Allowing control via the "keyboard interface" means that the content could be controlled through commands issued from the keyboard or by alternate methods that are capable of generating text as if a keyboard had been used.


Link refers to a hyperlink between the current document and a single destination. (Here, "link" refers to a single "arc" in the XML Linking Language (XLink) Version 1.0 specification.) Only links which are available to be activated by the user need to meet accessibility requirements. This excludes links that are activated automatically or programmatically.

marked in a way that the user can avoid its appearance

The content is marked in a fashion that would allow the user to determine that provocative material can be avoided. Some methods that might be used for this include:

  • metadata on the page

  • information in the title (so search engine shows it)

  • notification on the page before provocative information is encountered.

Editorial Note: This definition needs work.

media alternatives

Media alternatives present essential audio information visually (captions) and essential video information auditorily (audio descriptions).


For the purposes of these guidelines, multimedia refers to combined audio and video presentations.

Editorial Note: In the future, multimedia will likely be expanded to cover dynamic, interactive visual content and perhaps other combinations of media.

natural languages

Natural languages are those used by humans to communicate, including spoken, written, and signed languages.

non-text content

non-text content includes but is not limited to images, text in raster images, image map regions, animations (e.g., animated GIFs), ASCII art, images used as list bullets, spacers, graphical buttons, sounds (played with or without user interaction), stand-alone audio files, audio tracks of video, and video. It also includes any text that can not be translated into Unicode.


Scripts, applets, and programmatic objects are not covered in this definition and are addressed in guideline 4.2.


Required for conformance.

perceivable unit

The result of a user agent rendering the contents of a delivery unit. User agents may or may not render all information in a delivery unit. In some cases, a single delivery unit may be rendered as multiple perceivable units. For example, a single html file that is rendered as a set of presentation slides. Most perceivable units contain presentation and the means for interaction. However, for some devices such as printers, a perceivable unit may only contain presentation.


Presentation is the rendering of the content and structure in a form that can be sensed by the user.

programmatic user interface component

An interface component created by the author that is in addition to those provided by the user agent. For example, an HTML checkbox would not be a programmatic user interface component because the author is using an interface component supported by the user agent. A checkbox function implemented in script, however, would be a programmatic user interface component because it provides functionality that is not known or supported by user agents and can not be made accessible by user agents even if the user agent complied with UAAG.

programmatically determined

programmatically determined means that the specific value can be determined in a standard, machine or software readable form .

programmatically located

Programmatically located means that the value can be found, though there may be multiple possible values (for example, providing a dictionary definition for a word that has multiple meanings). This term contrasts with programmatically determined, where the specific value can be determined.

Editorial Note: This provision is dependent on the definition of a standard way to associate dictionaries and the availability of on-line dictionaries.

real-time events

Real-time events are those that are based on the occurrence of events in real-time where the events are not under the control of the author.

red flash threshold
  • A transition to or from a saturated red at any luminance level is not permitted when both of the following occur:

    1. the combined area of flashes occurring concurrently occupies more than one quarter of any 335 x 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels and

    2. there are more than three flashes within any one-second period.


    For the red flash threshold, a flash is defined as any pair of opposing transitions to or from a saturated red at any luminance level . (See note below)


Thresholds are based on ITC Guidance Note for Licensees on Flashing Images and Regular Patterns in Television (Revised and re-issued July 2001) as modified by the Wisconsin Computer Equivalence Algorithm.

regular expression

A regular expression as defined in XML Schema Part 2: Datatypes, Appendix F.

site navigation mechanism

A site navigation mechanism is a mechanism for easily orienting and moving about within the site. Site navigation mechanisms include but are not limited to:

  • A home page with hyperlinks on it and subsequent pages that link to the other pages at the site

  • site map(s)

  • search engine(s)

  • expanding outline(s)

  • dynamic fisheye views showing all linked pages or topics related to any page.

  • 3-D virtual representations of site content

spatial pattern thresholds

The international definitions for spatial pattern threshold are changing and we will adopt the new standards as they are released

  1. The way the parts of an authored unit are organized in relation to each other and;

  2. The way a collection of authored units is organized in relation to a delivery unit and;

  3. The way a collection of delivery units is organized


Editorial Note: Examples still need work. [Issue #506]

  1. A book is divided into chapters, paragraphs, lists, etc. Chapter titles help the reader anticipate the meaning of the following paragraphs. Lists clearly indicate separate, yet related ideas. All of these divisions help the reader anticipate changes in context.

  2. A bicycle is divided into wheels and a frame. Further, a wheel is divided into a tire and a rim. In an image of the bicycle, one group of circles and lines becomes "wheel" while another group becomes "frame."


Technology means a data format, programming or markup language, protocol or API.


A sequence of characters. Characters are those included in the Unicode/ISO/IEC 106464 repertoire. Refer to Characters (in Extensible Markup Language (XML) 1.1) for more information about the accepted character range.

text alternative

Text that is used in place of or in addition to non-text content.

text description

Editorial Note: We need to include a definition of text description here.

text label

Editorial Note: We need to include a definition of text label here.

time-dependent presentation

A time-dependent presentation is a presentation that

  • is composed of synchronized audio and visual tracks (e.g., a movie), OR

  • requires the user to respond interactively at specific times in the presentation.

unfamiliar content

Content might be unfamiliar if you are using terms specific to a particular community. For example, many of the terms used in this document are specific to the disability community.


Unicode is a universal character set that defines all the characters needed for writing the majority of living languages in use on computers. For more information refer to the Unicode Consortium or to Tutorial: Character sets & encodings in XHTML, HTML and CSS produced by the W3C Internationalization Activity.

URI pattern

A URI pattern is a regular expression identifying a set of resources. A resource belongs to the set if the regular expression matches its URI.


in order to be included in the set, the resource must exist; the regular expression may, and typically will, match URIs that do not refer to any existing resource.

user agent

In this document, the term "user agent" is used in two ways:

  1. The software and documentation components that together, conform to the requirements of the User Agent Accessibility Guidelines 1.0 (UAAG 1.0). This is the most common use of the term in this document and is the usage in the UAAG checkpoints.

  2. Any software that retrieves and renders Web content for users. This may include Web browsers, media players, plug-ins, and other programs — including assistive technologies — that help in retrieving and rendering Web content.


A time-based presentation that only contains video.

Wisconsin Computer Equivalence Algorithm

The Wisconsin Computer Equivalence Algorithm is a method for applying the United Kingdom's "ITC Guidance Note for Licensees on Flashing Images and Regular Patterns in Television (Revised and re-issued July 2001)" to content displayed on a computer screen, such as Web pages and other computer content. The ITC Guidance Document is based on the assumption that the television screen occupies the central ten degrees of vision. This is not accurate for a screen which is located in front of a person. The Wisconsin Algorithm basically carries out the same analysis as the ITC Guidelines except that is does it on every possible ten degree window for a prototypical computer display.

Editorial Note: Links to references will be provided when they become available.

Appendix B Contributors

Participants in the WCAG Working Group

Appendix C The differences between WCAG 1.0 and WCAG 2.0

Since the release of WCAG 1.0 in May 1999, the WCAG Working Group has received feedback on priorities of checkpoints, the usability of the set of documents, and requests for clarifications on the meaning of specific checkpoints and what is needed to satisfy them. Thus, it is intended that WCAG 2.0, when it eventually becomes a W3C Recommendation:

For a detailed comparison, refer to the Mapping Between WCAG 1.0 and the WCAG 2.0 Working Draft.

Improvements in WCAG 2.0

We hope that WCAG 2.0 will have several improvements over WCAG 1.0. While the primary goal of WCAG 2.0 is the same as WCAG 1.0 (to promote accessibility of Web content) additional goals for WCAG 2.0 include improvements that will:

  1. Ensure that requirements may be applied across technologies

  2. Ensure that the conformance requirements are clear

  3. Ensure that the deliverables are easy to use

  4. Write to a more diverse audience

  5. Clearly identify who benefits from accessible content

  6. Ensure that the revision is "backward compatible" with WCAG 1.0

For more information about the intended improvements in WCAG 2.0 Working Draft, please refer to Requirements for WCAG 2.0.

Appendix D References

Editorial Note: Links within the document will be turned into references and the links to those documents will be listed here. They are inline for the time being.