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     _________________________________________________________________
   
   W3C 
   
User Agent Accessibility Guidelines 1.0

W3C Candidate Recommendation, 12 September 2001

   This version:
          http://www.w3.org/TR/2001/CR-UAAG10-20010912/
          (Formats: single HTML, plain text, gzip PostScript, gzip PDF,
          gzip tar file of HTML, zip archive of HTML)
          
   Latest version:
          http://www.w3.org/TR/UAAG10/
          
   Previous version:
          http://www.w3.org/TR/2001/WD-UAAG10-20010622/
          
   Editors:
          Ian Jacobs, W3C
          Jon Gunderson, University of Illinois at Urbana-Champaign
          Eric Hansen, Educational Testing Service
          
   Authors and Contributors:
          See acknowledgements.
          
   Copyright © 1999 - 2001 W3C^® (MIT, INRIA, Keio), All Rights Reserved.
   W3C liability, trademark, document use and software licensing rules
   apply.
     _________________________________________________________________
   
Abstract

   This document provides guidelines for designing user agents that lower
   barriers to Web accessibility for people with disabilities (visual,
   hearing, physical, and cognitive). User agents include HTML browsers
   and other types of software that retrieve and render Web content. A
   user agent that conforms to these guidelines will promote
   accessibility through its own user interface and through other
   internal facilities, including its ability to communicate with other
   technologies (especially assistive technologies). Furthermore, all
   users, not just users with disabilities, are expected to find
   conforming user agents to be more usable.
   
   In addition to helping developers of HTML browsers, media players,
   etc., this document will also benefit developers of assistive
   technologies because it explains what types of information and control
   an assistive technology may expect from a conforming user agent.
   Technologies not addressed directly by this document (e.g.,
   technologies for braille rendering) will be essential to ensuring Web
   access for some users with disabilities.
   
Status of this document

   This section describes the status of this document at the time of its
   publication. Other documents may supersede this document. The latest
   status of this document series is maintained at the W3C.
   
   This is the 12 September 2001 Candidate Recommendation of "User Agent
   Accessibility Guidelines 1.0". W3C publishes a technical report as a
   Candidate Recommendation to indicate that the document is believed to
   be stable, and to encourage implementation by the developer community.
   Candidate Recommendation status is described in section 5.2.3 of the
   Process Document. The UAWG resolved to request to advance to Candidate
   Recommendation at its 30 August 2001 teleconference.
   
   The User Agent Accessibility Guidelines Working Group (UAWG) expects
   to request that the Director advance this document to Proposed
   Recommendation once the Working Group has demonstrated two
   implementations of each requirement. The UAWG, working closely with
   the developer community, expects to show these implementations by the
   end of December 2001. This estimate is based on the UAWG's initial
   implementation report. The UAWG expects to revise this report over the
   course of the implementation period.
   
   This document incorporates resolutions of the User Agent Accessibility
   Guidelines Working Group to all issues raised during the third last
   call review of the 9 April 2001 version. A snapshot of the third last
   call issues list is available, as is the disposition of comments
   (which includes objections).
   
   A list of changes to this document is available.
   
   Publication as a Candidate Recommendation 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."
   
   Please send comments about this document to the public mailing list
   w3c-wai-ua@w3.org; public archives are available.
   
   This document is part of a series of accessibility documents published
   by the Web Accessibility Initiative (WAI) of the World Wide Web
   Consortium (W3C). WAI Accessibility Guidelines are produced as part of
   the WAI Technical Activity. The goals of the User Agent Accessibility
   Guidelines Working Group are described in the charter.
   
   A list of current W3C Recommendations and other technical documents
   can be found at the W3C Web site.
   
Table of contents

     * Abstract
     * Status of this document
     * 1. Introduction
          + 1.1 Relationship to WAI accessibility guidelines
          + 1.2 Target user agents
          + 1.3 Known limitations of this document
          + 1.4 Relationship to general software design guidelines
     * 2. The user agent accessibility guidelines
          + 1. Support input and output device-independence.
          + 2. Ensure user access to all content.
          + 3. Allow configuration not to render some content that may
            reduce accessibility.
          + 4. Ensure user control of rendering.
          + 5. Ensure user control of user interface behavior.
          + 6. Implement interoperable application programming
            interfaces.
          + 7. Observe operating environment conventions.
          + 8. Implement specifications that benefit accessibility.
          + 9. Provide navigation mechanisms.
          + 10. Orient the user.
          + 11. Allow configuration and customization.
          + 12. Provide accessible user agent documentation and help.
     * 3. Conformance
          + 3.1 Unconditional conformance
          + 3.2 Conditional conformance
          + 3.3 Conformance details
          + 3.4 Conformance levels
          + 3.5 Content type labels
          + 3.6 Input modality labels
          + 3.7 Selection label
          + 3.8 Checkpoint applicability
          + 3.9 Well-formed conformance claims
          + 3.10 Validity of a claim
     * 4. Glossary
     * 5. References
          + 5.1 How to refer to this document
          + 5.2 Normative references
          + 5.3 Informative references
     * 6. Acknowledgments
       
   An appendix to this document [UAAG10-SUMMARY] summarizes the
   document's principal goals and structure.
   
   Another appendix to this document [UAAG10-CHECKLIST] lists all
   checkpoints for convenient reference (e.g., as a tool for developers
   to evaluate software for conformance).
   
   Note: With a user agent that implements HTML 4 [HTML4] access keys,
   readers may navigate directly to the table of contents via the "c"
   character. Users may have to use additional keyboard strokes depending
   on their operating environment.
   
Related resources

   A separate document, entitled "Techniques for User Agent Accessibility
   Guidelines 1.0" [UAAG10-TECHS], provides suggestions and examples of
   how each checkpoint might be satisfied. It also includes references to
   other accessibility resources (such as platform-specific software
   accessibility guidelines) that provide additional information on how a
   user agent may satisfy each checkpoint. The techniques provided in
   "Techniques for User Agent Accessibility Guidelines 1.0" are
   informative examples only, and other strategies may be used or
   required to satisfy the checkpoints. The Techniques document is
   expected to be updated more frequently than the current guidelines.
   Developers, W3C Working Groups, users, and others are encouraged to
   contribute techniques for incorporation into the Techniques document.
   
   The Web Accessibility Initiative provides other resources and
   educational materials to promote Web accessibility. Resources include
   information about accessibility policies, links to translations of WAI
   materials into languages other than English, information about
   specialized user agents and other tools, accessibility training
   resources, and more.
     _________________________________________________________________
   
1. Introduction

   This document specifies requirements that, if satisfied by user agent
   developers, will lower barriers to accessibility. This introduction
   (section 1) provides context for understanding the guidelines listed
   in section 2. Section 1 explains the relationship of this document to
   other accessibility guidelines published by the Web Accessibility
   Initiative, which user agents are expected to conform, known
   limitations of this document, and the relationship of this document to
   other software design guidelines. Section 3 explains how to make
   claims that software conforms to these guidelines and details about
   the applicability of the requirements for different kinds of user
   agents.
   
  1.1 Relationship to WAI accessibility guidelines
  
   "User Agent Accessibility Guidelines 1.0" (UAAG 1.0) is part of a
   series of accessibility guidelines published by the Web Accessibility
   Initiative (WAI). The documents in this series reflect an
   accessibility model in which Web content authors, format designers,
   and software developers have roles in ensuring that users with
   disabilities have access to the Web. These stakeholders intersect and
   complement each other as follows:
     * Protocol (e.g., HTTP) and content format (e.g., HTML, XHTML, XML,
       SVG, SMIL, MathML, etc.) specifications allow communication on the
       Web. Format designers include features that authors should use to
       create accessible content, and features that user agents should
       support through an accessible user interface.
     * Authors make use of the accessibility features of different format
       specifications, use markup appropriately, write in clear and
       simple language, organize a Web site consistently, etc. The "Web
       Content Accessibility Guidelines 1.0" [WCAG10] explains the
       responsibilities of authors in meeting the needs of users with
       disabilities. The "Web Content Accessibility Guidelines (WCAG)
       1.0" is considered the reference for what defines accessible Web
       content. The "Authoring Tool Accessibility Guidelines 1.0"
       [ATAG10] explains the responsibilities of authoring tool
       developers. An accessible authoring tool facilitates the creation
       of accessible Web content and may be operated by users with
       disabilities.
     * User agent developers design software that conforms to
       specifications (including implementation of their accessibility
       features), provides an accessible user interface, accessible
       documentation, and communicates with other software (notably
       assistive technologies).
       
   This document explains the responsibilities of user agents in meeting
   the needs of users with disabilities. The requirements of this
   document interact with those of the "Web Content Accessibility
   Guidelines 1.0" [WCAG10] in a number of ways:
     * UAAG 1.0 checkpoint 8.1 requires implementation of the
       accessibility features of all implemented specifications. Features
       are those identified as such and those that satisfy all of the
       requirements of WCAG 1.0 [WCAG10].
     * UAAG 1.0 checkpoint 12.1 requires conformance to WCAG 1.0 for user
       agent documentation.
     * UAAG 1.0 also incorporates some terms and concepts from WCAG 1.0,
       a natural consequence of fact that the documents were designed to
       complement one another.
       
   Formats, authors, and designers all have limitations. Formats
   generally do not enable authors to encode all of their knowledge in a
   way that a user agent can recognize 100%. A format may lack features
   required for accessibility. An author may not make use of the
   accessibility features of a format or may misuse a format (which can
   cause problems for user agents). A user agent designer may not
   implement a format specification correctly or completely. Some
   requirements of this document take these limitations into account.
     * UAAG 1.0 includes requirements to satisfy the expectations set by
       WCAG 1.0 "until user agent" clauses. These clauses make additional
       requirements of authors in order to compensate for some
       limitations of deployed user agents.
     * UAAG 1.0 includes several repair requirements (e.g., checkpoints
       checkpoint 2.7 and checkpoint 2.11) for cases where content does
       not conform to WCAG 1.0. Furthermore, this document includes some
       requirements to address certain widespread authoring practices
       that are discouraged because they may cause accessibility or
       usability problems (e.g., some uses of HTML frames).
     * Except for the indicated repair checkpoints, UAAG 1.0 only
       requires user agents to handle what may be recognized through
       protocols and formats. For example, user agents are not expected
       to recognize that the author has used "clear and simple" language
       to express ideas. Please see the section on checkpoint
       applicability for more information about what the user agent is
       expected to recognize.
       
  1.2 Target user agents
  
   This document was designed specifically to improve the accessibility
   of user agents with multimedia capabilities running in the following
   type of environment (typically that of a desktop computer):
     * The operating environment includes a keyboard;
     * Assistive technologies may be used in the operating environment
       and may communicate with the conforming user agent;
       
   This document is not designed so that user agents on other types of
   platforms (e.g., handheld devices, kiosks, etc.) will readily conform.
   This document does not forbid conformance by any user agent, but some
   requirements (e.g., implementation of certain APIs) are not likely to
   be satisfied on environments other than the target environment. Future
   work by the UAWG may address the accessibility of user agents running
   on handheld devices, etc.
   
   The target user agent is one designed for the general public to handle
   general-purpose content in ordinary operating conditions. It is
   expected that a conforming user agent will typically consist of a Web
   browser, one or more media players, and possibly other components.
   
   This document was designed to improve the accessibility of target user
   agents for users with one or more disabilities (including visual,
   hearing, physical, and cognitive) in two ways:
    1. through its own user interface, and
    2. through other internal facilities, including its ability to
       communicate with other technologies (especially assistive
       technologies).
       
   Technologies not addressed directly by this document (e.g., those for
   braille rendering) will be essential to ensuring Web access for some
   users with disabilities. Note that the ability of conforming user
   agents to communicate well with assistive technologies will depend in
   part on the willingness of assistive technology developers to follow
   the same standards and conventions for communication.
   
   This document allows a certain amount of flexibility in the features a
   user agent must support in order to conform. For example, some user
   agents may conform even though they do not support certain content
   types (such as video or audio) or input modalities (such as mouse or
   voice). See the section on conformance for more information.
   
  1.3 Known limitations of this document
  
   People with (or without) disabilities access the Web with widely
   varying sets of capabilities, software, and hardware. Some users with
   disabilities:
     * May not be able to see, hear, move, speak, or may not be able to
       process some types of information easily or at all.
     * May have difficulty reading or comprehending text.
     * May not have or be able to use a keyboard or pointing device.
       
   This document does not include requirements to meet all known
   accessibility needs. Some known limitations of this document include
   the following:
     * Input modalities. This document only includes requirements for
       keyboard, pointing device, and voice input modalities. This
       document includes several checkpoints related to voice input as
       part of general input requirements (e.g., the checkpoints of
       guideline 7 and guideline 11) but does not otherwise address
       voice-based navigation or control. Note: The UAWG intends to
       coordinate further work on the topics of voice input and
       synthesized speech rendering with groups in W3C's Voice Browser
       Activity.
     * Output modalities. This document does not include requirements for
       braille rendering. Some requirements are specific to graphical
       rendering and others specific to synthesized speech rendering
       (speech rendering requirements are made by checkpoint 4.12 to
       checkpoint 4.16). Many of the requirements of this document are
       generic enough to apply to any output modality (including
       braille). User agents conform to this document by supporting some
       combination of graphical and audio/speech rendering output; see
       the section on content type labels for more information.
     * Size and color of non-text content. This document includes some
       checkpoints to ensure that the user is able to control the size
       and color of visually rendered text content (checkpoints 4.1 and
       4.3). This document does not in general address control of the
       size and color of visually rendered non-text content. Note:
       Resizing capabilities may be required for conformance to other
       specifications (e.g., SVG [SVG]).
     * Background image interference. The requirement of checkpoint 3.1
       to allow the user to turn off rendering of background images does
       not extend to multi-layered rendering.
     * User control of every user interface component. This document
       includes some requirements for user control of user interface
       components that may be changed through content (see guideline 5).
       However, these requirements do not account for every user
       interface component that the author may affect (e.g., the author
       might supply a script that causes text to scroll in the status
       bar). User agents are required to follow software usability
       guidelines (see checkpoint 7.3), which are also expected to
       include requirements for user control over user interface
       behavior. Note. It is more difficult for users to distinguish
       content from user interface when both are rendered as sound in one
       dimension, than it is when both are rendered visually in two
       dimensions. Developers of aural user agents are therefore strongly
       encouraged to apply the requirements of this document to both
       content and user agent components.
     * Time. This document includes requirements for control of some time
       parameters (including checkpoint 2.4, checkpoint 4.4, checkpoint
       4.5, and checkpoint 4.12). The requirements are for time
       parameters that the user agent recognizes and controls. This
       document does not include requirements for control of time
       parameters managed on the server.
     * Security. This document does not address security issues that may
       arise as a result of these requirements. For instance,
       requirements that software be able to read and write content and
       user interface information through APIs raise security issues. See
       the section on restricted functionality and conformance.
     * Intellectual property. This document does not address intellectual
       property issues that may arise as a result of these requirements.
       
   Note: The User Agent Accessibility Guidelines Working Group may
   address these topics in a future version of the User Agent
   Accessibility Guidelines. Even though UAAG 1.0 does not address these
   topics, user agent developers are encouraged to consider them in their
   designs.
   
  1.4 Relationship to general software design guidelines
  
   Considerable effort has been made to ensure that the requirements of
   this document are compatible with other good software design
   practices. However, this document does not purport to be a complete
   guide to good software design. For instance, the general topic of user
   interface design for computer software exceeds the scope of this
   document, though some user interface requirements have been included
   because of their importance to accessibility. The "Techniques for User
   Agent Accessibility Guidelines 1.0" [UAAG10-TECHS] includes some
   references to general software design guidelines and platform-specific
   accessibility guidelines (see checkpoint 7.3). Involving people with
   disabilities in the design and testing of software will generally
   improve the accessibility of the software.
   
   Installation is an important aspect of both accessibility and general
   software usability. On platforms where a user can install a user
   agent, the installation (and update) procedures need to be accessible.
   This document does not include a checkpoint requiring that
   installation procedures be accessible. Since this document considers
   installation to be part of software usage, the different aspects of
   installation (user interface, documentation, operating environment
   conventions, etc.) are already covered by the complete set of
   checkpoints.
   
    Benefits of accessible user agent design
    
   Many users without disabilities are likely to benefit from the
   requirements developed to benefit users with disabilities. For
   example, users without disabilities:
     * may have a text-only screen, a small screen, or a slow Internet
       connection (e.g., via a mobile phone browser). These users are
       likely to benefit from the same features that provide access to
       people with low vision or blindness.
     * may be in a situation where their eyes, ears, or hands are busy or
       interfered with (e.g., driving to work, working in a noisy
       environment, etc.). These users are likely to benefit from the
       same features that provide access to people who cannot use a mouse
       or keyboard due to a visual, hearing, or physical disability.
     * may not understand fluently the natural language of spoken
       content. These users are likely to benefit from the same visual
       rendering of text equivalents that make spoken language accessible
       to people with a hearing disability.
       
   Software that satisfies the requirements of this document is expected
   to be more flexible, manageable, extensible, and beneficial to all
   users. For example, a user agent architecture that allows programmatic
   access to content and the user interface will encourage software
   modularity and reuse, and will enable operation by scripting tools and
   automated test engines in addition to assistive technologies.
   
2. The user agent accessibility guidelines

   The twelve guidelines in this document state general principles for
   the development of accessible user agents. Each guideline includes:
     * The guideline number.
     * The statement of the guideline.
     * The rationale behind the guideline and identification of some
       groups of users who benefit from it.
     * A list of checkpoint definitions. This list may be split into
       groups of related checkpoints. For instance, the list might be
       split into one group of "checkpoints for visually rendered text"
       and second group of "checkpoints for audio volume control"."
       Within each group, checkpoints are ordered according to their
       priority, e.g., Priority 1 before Priority 2. Within a guideline,
       checkpoint groupings and checkpoint order have no bearing on
       conformance.
       
   Each checkpoint definition includes the following parts. Some parts
   are normative (i.e., relate to conformance); others are informative
   only.
     * The checkpoint number.
     * The checkpoint title. This title is not a requirement, just a
       phrase to help readers remember an important requirement made by
       the checkpoint statement. (Informative)
     * The priority of the checkpoint. (Normative)
     * The statement or statements of the checkpoint. These statements
       include one or more requirements that must be satisfied by the
       user agent (i.e., the "subject of the claim) for the purposes of
       conformance. (Normative)
     * An optional "content/rendered content/user agent feature/both"
       label that indicates whether the requirements of the checkpoint
       must be satisfied by the subject of the claim for all content, all
       rendered content, for user agent features only, or for both
       content and user agent features. The label only appears when
       necessary to disambiguate the checkpoint. (Normative)
     * A link to rationale, implementation details, references, and more
       information in "Techniques for User Agent Accessibility Guidelines
       1.0" [UAAG10-TECHS]. (Informative)
     * Content type labels (zero or more). Content type labels are
       explained in the section on conformance. (Normative)
     * Optional notes about the checkpoint (beginning with the word
       "Note"). They notes clarify the scope of the checkpoint through
       further description, examples, cross references, and commentary.
       Some checkpoints in this document are more general than others,
       and some may overlap in scope. Therefore, a checkpoint may be
       identified as a "special case" or an "important special case" of
       one or more other checkpoints. (Informative)
       
   Each checkpoint definition expresses one or more requirements. These
   requirements are not technology specific. In fact, they have been
   designed to be largely technology independent, in order to make sense
   for a variety of existing and future technologies. "Techniques for
   User Agent Accessibility Guidelines 1.0" [UAAG10-TECHS] is an
   important resource to help developers understand how to "apply" the
   requirements to HTML, CSS, SMIL, and SVG, and several operating
   environments. The User Agent Accessibility Guidelines Working Group
   welcomes comments and anticipates discussion on how to apply these
   requirements to new technologies in different operating environments.
   
   Each requirement is a "minimal" requirement, which means that for
   conformance, the user agent is required to satisfy no more than the
   stated requirement. In many cases, however, it may be easier or less
   costly (or just be better design) to implement a general feature that
   satisfies more than a minimal requirement. One general solution might
   satisfy five checkpoints and be easier to implement than five
   disconnected features. For instance, a navigable structure view of
   content that allows users to query elements for their properties is
   likely to benefit all users and may be used to satisfy a number of
   requirements of this document.
   
   Some requirements have a wider impact than others. For instance, the
   keyboard requirements of checkpoint 1.1 have an impact on all other
   requirements in the document related to user input: any requirement
   that involves user input must be satisfied through the keyboard.
   Because the keyboard requirements of checkpoint 1.1 have been factored
   out, the other checkpoints are shorter; they are written "Allow
   configuration" instead of "Allow configuration through the keyboard."
   First-time readers of the document are encouraged to read the full
   context provided for each checkpoint, including the guideline prose,
   the surrounding checkpoints (since nearby checkpoints are generally
   related), notes after checkpoints, and associated techniques (in the
   Techniques document [UAAG10-TECHS]). The checklist [UAAG10-CHECKLIST]
   is also a useful tool (e.g., for evaluating a user agent for
   conformance), but does not provide the same contextual support.
   
  Priorities
  
   Each checkpoint in this document is assigned a priority that indicates
   its importance for users with disabilities.
   
   Priority 1 (P1)
          This checkpoint must be satisfied by user agents, otherwise one
          or more groups of users with disabilities will find it
          impossible to access the Web. Satisfying this checkpoint is a
          basic requirement for enabling some people to access the Web.
          
   Priority 2 (P2)
          This checkpoint should be satisfied by user agents, otherwise
          one or more groups of users with disabilities will find it
          difficult to access the Web. Satisfying this checkpoint will
          remove significant barriers to Web access for some people.
          
   Priority 3 (P3)
          This checkpoint may be satisfied by user agents to make it
          easier for one or more groups of users with disabilities to
          access information. Satisfying this checkpoint will improve
          access to the Web for some people.
          
Guideline 1. Support input and output device-independence.

    Ensure that the user can interact with the user agent (and the content it
    renders) through different input and output devices.
    
   Since people use a variety of devices for input and output, user agent
   developers need to ensure redundancy in the user interface. The user
   may have to operate the user interface with a variety of input devices
   (keyboard, pointing device, voice input, etc.) and output modalities
   (e.g., graphical, speech, or braille rendering).
   
   Though it may seem contradictory, enabling full user agent operation
   through the keyboard is an important part of promoting
   device-independence given today's user agents. In addition to the fact
   that some form of keyboard is supported by most platforms, there are
   several reasons for this:
     * For some users (e.g., users with blindness or physical
       disabilities), operating a user agent with a pointing device may
       be difficult or impossible since it requires tracking the pointing
       device position in a two-dimensional visual space. Keyboard
       operation does not generally require as much movement "through
       space".
     * Some assistive technologies that support a diversity of input and
       output mechanisms use keyboard APIs for communication with some
       user agents; see checkpoint 6.6. People who cannot or do not use a
       pointing device may interact with the user interface with the
       keyboard, through voice input, a head wand, touch screen, or other
       device.
       
   While this document only requires keyboard operation for conformance,
   it promotes device-independence by also allowing people to claim
   conformance for full pointing device support or full voice support.
   
   As a way to promote output device independence, this guideline
   requires support for text messages in the user interface because text
   may be rendered visually, as synthesized speech, and as braille.
   
   The API requirements of guideline 6 also promote device independence
   by ensuring communication with specialized software.
   
    Checkpoints
    
      1.1 Full keyboard access. (P1)
      
    1. Ensure that the user can operate through keyboard input alone any
       user agent functionality available through the user interface.
       
   For both content and user agent. Techniques for checkpoint 1.1
   
   Note: User agents may support at least two types of keyboard access to
   functionalities: direct access (where user awareness of a location "in
   space" is not required, as is the case with keyboard shortcuts and
   navigation of user agent menus) and spatial access (where the user
   moves the pointing device "in space" via the keyboard). To satisfy
   this checkpoint, user agents are expected to provide a mix of both
   types of keyboard access. User agents should allow direct keyboard
   access where possible, and this may be redundant with spatial input
   techniques. Furthermore, the user agent should satisfy this
   requirement by offering a combination of keyboard-operable user
   interface controls (e.g., keyboard operable print menus and settings)
   and direct keyboard operation of user agent functionalities (e.g., a
   short cut to print the current page). As examples of functionalities,
   ensure that the user can interact with enabled elements, select
   content, navigate viewports, configure the user agent, access
   documentation, install the user agent, operate controls of the user
   interface, etc., all entirely through keyboard input. It is also
   possible to claim conformance to this document for full support
   through pointing device input and voice input. See the section on
   input modality labels.
   
      1.2 Activate event handlers. (P1)
      
    1. For the element with content focus, allow the user to activate any
       explicitly associated input device event handlers through keyboard
       input alone.
    2. The user agent is not required to allow activation of event
       handlers associated with a given device (e.g., the pointing
       device) in any order other than what the device itself allows.
       
   Techniques for checkpoint 1.2
   
   Note: The requirements for this checkpoint refer to any explicitly
   associated input device event handlers associated with an element,
   independent of the input modalities for which the user agent conforms.
   For example, suppose that an element has an explicitly associated
   handler for pointing device events. Even when the user agent only
   conforms for keyboard input (and does not conform for the pointing
   device, for example), this checkpoint requires the user agent to allow
   the user to activate that handler with the keyboard. This checkpoint
   is an important special case of checkpoint 1.1. Please refer to the
   checkpoints of guideline 9 for more information about focus
   requirements.
   
      1.3 Provide text messages. (P1)
      
    1. Ensure that every message (e.g., prompt, alert, notification,
       etc.) that is a non-text element and is part of the user agent
       user interface has a text equivalent.
       
   Techniques for checkpoint 1.3
   
   Note: For example, if the user is alerted of an event by an audio cue,
   a visually-rendered text equivalent in the status bar could satisfy
   this checkpoint. Per checkpoint 6.4, a text equivalent for each such
   message must be available through an API. See also checkpoint 6.5 for
   requirements for programmatic alert of changes to the user interface.
   
   [next guideline 2] [review guideline 1] [contents]
   
Guideline 2. Ensure user access to all content.

    Ensure that users have access to all content, notably conditional content
    that may have been provided to meet the requirements of the Web Content
    Accessibility Guidelines 1.0 [WCAG10].
    
   The checkpoints in this section require the user agent to provide
   access to all content through a series of complementary mechanisms
   designed so that if one fails, another will provide some access. The
   following preferences are embodied in the checkpoints:
     * Not all content is rendered at all times. Automatic decision by
       the user agent about when and where to render conditional content
       is preferred, but manual choice by the user may be necessary for
       access.
     * Structure is preferred (both the author's specified preferences
       and the user's structured access), but unstructured access may be
       necessary for access to all content.
     * Rendering according to format specification is preferred, but a
       source view of text content may be necessary for access (e.g.,
       because of user-side error conditions, authoring errors,
       inadequate specification, or incorrect user agent implementation).
       For example, the user may have to look at URIs for information,
       HTML comments, XML element names, or script data. The user agent
       should respect authoring synchronization cues for content that
       changes over time, but also needs to allow the user to control the
       time intervals when user input is possible.
     * Configuration and control of rendering are important for access.
       
   Authors may use the conditional content mechanisms of a specification
   to satisfy the requirements of the Web Content Accessibility
   Guidelines 1.0 [WCAG10]. Ensuring access to conditional content
   benefits all users since some users may not have access to some
   content due to a technological limitation (e.g., their mobile browser
   cannot display graphics) or simply a configuration preference (e.g.,
   they have a slow Internet connection and prefer not to download movies
   or images).
   
    Checkpoints
    
      2.1 Render content according to specification. (P1)
      
    1. Render content according to format specification (e.g., for a
       markup language or style sheet).
    2. When a rendering requirement of another specification contradicts
       a requirement of the current document, the user agent may
       disregard the rendering requirement of the other specification and
       still satisfy this checkpoint.
    3. Rendering requirements include format-defined interactions between
       author preferences and user preferences/capabilities (e.g., when
       to render the "alt" attribute in HTML, the rendering order of
       nested OBJECT elements in HTML, test attributes in SMIL, and the
       cascade in CSS2).
       
   Techniques for checkpoint 2.1
   
   Note: If a conforming user agent does not render a content type, it
   should allow the user to choose a way to handle that content (e.g., by
   launching another application, by saving it to disk, etc.). The user
   agent is not required to satisfy this checkpoint for all implemented
   specifications; see the section on conformance and implementing
   specifications for more information.
   
      2.2 Provide text view. (P1)
      
    1. For content authored in text formats, provide a view of the text
       source. For the purposes of this document, text formats are
       defined to be:
          + all media objects given an Internet media type of "text"
            (e.g., text/plain, text/HTML, or text/*) as defined in RFC
            2046 [RFC2046], section 4.1.
          + all SGML and XML applications, regardless of Internet media
            type (e.g., HTML 4.01, XHTML 1.1, SMIL, SVG, etc.).
       
   Techniques for checkpoint 2.2
   
   Note: A user agent would also satisfy this checkpoint by providing a
   source view for any text format, not just implemented text formats.
   The user agent is not required to satisfy this checkpoint for all
   implemented specifications; see the section on conformance and
   implementing specifications for more information.
   
      2.3 Render conditional content. (P1)
      
    1. Allow configuration to provide access to each piece of unrendered
       conditional content "C".
    2. The configuration may be a switch that, for all content, turns on
       or off the access mechanisms described in the next provision.
    3. When a specification does not explain how to provide access to
       this content, do so as follows:
          + If C is a summary, title, alternative, description, or
            expansion of another piece of content D, provide access
            through at least one of the following mechanisms:
               o (1a) render C in place of D;
               o (2a) render C in addition to D;
               o (3a) provide access to C by querying D. In this case,
                 the user agent must also alert the user, on a
                 per-element basis, to the existence of C (so that the
                 user knows to query D);
               o (4a) allow the user to follow a link to C from the
                 context of D.
          + Otherwise, provide access to C through at least one of the
            following mechanisms:
               o (1b) render a placeholder for C, and allow the user to
                 view the original author-supplied content associated
                 with each placeholder;
               o (2b) provide access to C by query (e.g., allow the user
                 to query an element for its attributes). In this case,
                 the user agent must also alert the user, on a
                 per-element basis, to the existence of C;
               o (3b) allow the user to follow a link in context to C.
    4. To satisfy this checkpoint, the user agent may provide access on a
       per-element basis (e.g., by allowing the user to query individual
       elements) or for all elements (e.g., by offering a configuration
       to render conditional content all the time).
       
   For all content. Techniques for checkpoint 2.3
   
   Note: For instance, an HTML user agent might allow users to query each
   element for access to conditional content supplied for the "alt",
   "title", and "longdesc" attributes. Or, the user agent might allow
   configuration so that the value of the "alt" attribute is rendered in
   place of all IMG elements (while other conditional content might be
   made available through another mechanism). See checkpoint 2.10 for
   additional placeholder requirements.
   
      2.4 Allow time-independent interaction. (P1)
      
    1. For rendered content where user input is only possible within a
       finite time interval controlled by the user agent, allow
       configuration to provide a view where user interaction is
       time-independent.
    2. The user agent may satisfy this checkpoint by pausing processing
       automatically to allow for user input, and resuming processing on
       explicit user request. When this technique is used, pause at the
       end of each time interval where user input is possible. In the
       paused state:
          + Alert the user that the rendered content has been paused
            (e.g., highlight the "pause" button in a multimedia player's
            control panel).
          + Highlight which enabled elements are time-sensitive.
          + Allow the user to interact with the enabled elements.
          + Allow the user to resume on explicit user request (e.g., by
            pressing the "play" button in a multimedia player's control
            panel; see also checkpoint 4.5).
    3. The user agent may satisfy this checkpoint by generating a
       time-independent ("static") view, based on the original content,
       that offers the user the same opportunities for interaction. The
       static view should reflect the structure and flow of the original
       time-sensitive presentation; orientation cues will help users
       understand the context for various interaction opportunities.
    4. When satisfying this checkpoint for a real-time presentation, the
       user agent may discard packets that continue to arrive after the
       construction of the time-independent view (e.g., when paused or
       after the construction of a static view).
       
   Techniques for checkpoint 2.4
   
   Note: If the user agent satisfies this checkpoint by pausing
   automatically, it may be necessary to pause more than once when there
   are multiple opportunities for time-sensitive user interaction When
   pausing, pause synchronized content as well (whether rendered in the
   same or different viewports) per checkpoint 2.6. In SMIL 1.0 [SMIL],
   for example, the "begin", "end", and "dur" attributes synchronize
   presentation components. This checkpoint does not apply when the user
   agent cannot recognize the time interval in the presentation format,
   or when the user agent cannot control the timing (e.g., because it is
   controlled by the server). See also checkpoint 3.5, which involves
   client-driven content refresh.
   
      2.5 Make captions, transcripts available. (P1)
      
    1. Allow configuration or control to render text transcripts,
       collated text transcripts, captions, and auditory descriptions at
       the same time as the associated audio tracks and visual tracks.
       
   For all content. Techniques for checkpoint 2.5
   
   Content type labels: Video, Audio.
   
   Note: This checkpoint is an important special case of checkpoint 2.1.
   
      2.6 Respect synchronization cues. (P1)
      
    1. Respect synchronization cues (e.g., in markup) during rendering.
       
   Techniques for checkpoint 2.6
   
   Content type labels: Video, Audio.
   
   Note: This checkpoint is an important special case of checkpoint 2.1.
   
      2.7 Repair missing content. (P2)
      
    1. Allow configuration to generate repair text when the user agent
       recognizes that the author has failed to provide conditional
       content that was required by the format specification.
    2. The user agent may satisfy this checkpoint by basing the repair
       text on any of the following available sources of information: URI
       reference, content type, or element type.
       
   For all content. Techniques for checkpoint 2.7
   
   Note: Some markup languages (such as HTML 4 [HTML4] and SMIL 1.0
   [SMIL] require the author to provide conditional content for some
   elements (e.g., the "alt" attribute on the IMG element). Repair text
   based on URI reference, content type, or element type is sufficient to
   satisfy the checkpoint, but may not result in the most effective
   repair. Information that may be recognized as relevant to repair might
   not be "near" the missing conditional content in the document object.
   For instance, instead of generating repair text on a simple URI
   reference, the user agent might look for helpful information near a
   different instance of the URI reference in the same document object,
   or might retrieve useful information (e.g., a title) from the resource
   designated by the URI reference.
   
      2.8 No repair text. (P3)
      
    1. Allow at least two configurations for when the user agent
       recognizes that conditional content required by the format
       specification is present but empty:
          + generate no repair text, or
          + generate repair as described in checkpoint 2.7.
       
   For all content. Techniques for checkpoint 2.8
   
   Note: In some authoring scenarios, empty content (e.g., a string of
   zero characters) may make an appropriate text equivalent, such as when
   non-text content has no other function than pure decoration, or when
   an image is part of a "mosaic" of several images and doesn't make
   sense out of the mosaic. Please refer to the Web Content Accessibility
   Guidelines 1.0 [WCAG10] for more information about text equivalents.
   
      2.9 Render conditional content automatically. (P3)
      
    1. Allow configuration to render all conditional content
       automatically. The user agent is not required to render all
       conditional content at the same time in a single viewport.
    2. Provide access to this content according to format specifications
       or where unspecified, by applying one of the techniques described
       in checkpoint 2.3: 1a, 2a, or 1b.
       
   For all content. Techniques for checkpoint 2.9
   
   Note: For instance, an HTML user agent might allow configuration so
   that the value of the "alt" attribute is rendered in place of all IMG
   elements (while other conditional content might be made available
   through another mechanism). The user agent may offer multiple
   configurations (e.g., a first configuration to render one type of
   conditional content automatically, a second to render another type,
   etc.).
   
      2.10 Toggle placeholders. (P3)
      
    1. Once the user has viewed the original author-supplied content
       associated with a placeholder, allow the user to turn off the
       rendering of the author-supplied content.
       
   Techniques for checkpoint 2.10
   
   Note: For example, if the user agent substitutes the author-supplied
   content for the placeholder in context, allow the user to "toggle"
   between placeholder and the associated content. Or, if the user agent
   renders the author-supplied content in a separate viewport, allow the
   user to close that viewport. Note: See checkpoint 2.3, provision (1b)
   for placeholder requirements.
   
      2.11 Alert unsupported language. (P3)
      
    1. Allow configuration not to render content in unsupported natural
       languages, when that content would otherwise be rendered. Content
       "in a natural language" includes pre-recorded spoken language and
       text in a given script, i.e., writing system.
    2. Indicate to the user in context that author-supplied content has
       not been rendered.
    3. This checkpoint does not require the user agent to allow different
       configurations for different natural languages.
       
   Techniques for checkpoint 2.11
   
   Note: For example, use a text substitute or accessible graphical icon
   to indicate that content in a particular language has not been
   rendered.
   
   [next guideline 3] [review guideline 2] [previous guideline 1]
   [contents]
   
Guideline 3. Allow configuration not to render some content that may reduce
accessibility.

    Ensure that the user may turn off rendering of content (audio, video,
    scripts, etc.) that may reduce accessibility by obscuring other content or
    disorienting the user.
    
   Some content or behavior specified by the author may make the user
   agent unusable or may obscure information. For instance, flashing
   content may trigger seizures in people with photosensitive epilepsy,
   or may make a Web page too distracting to be usable by someone with a
   cognitive disability. Blinking text can affect screen reader users,
   since screen readers (in conjunction with speech synthesizers or
   braille displays) may re-render the text every time it blinks.
   Distracting background images, colors, or sounds may make it
   impossible for users to see or hear other content. Dynamically
   changing Web content may cause problems for some assistive
   technologies. Scripts that cause unanticipated changes (viewports that
   open, automatically redirected or refreshed pages, etc.) may disorient
   some users with cognitive disabilities.
   
   This guideline requires the user agent to allow configuration so that,
   when loading Web resources, the user agent does not render content in
   a manner that may pose accessibility problems. Requirements for
   interactive control of rendered content are part of guideline 4.
   
    Checkpoints
    
      3.1 Toggle background images. (P1)
      
    1. Allow configuration not to render background image content.
    2. In this configuration, the user agent is not required to retrieve
       background images from the Web.
    3. This checkpoint only requires control of background images for
       "two-layered renderings", i.e., one rendered background image with
       all other content rendered "above it".
       
   Techniques for checkpoint 3.1
   
   Content type labels: Image.
   
   Note: See checkpoint 2.3 for information about how to provide access
   to unrendered background images. When background images are not
   rendered, user agents should render a solid background color instead
   (see checkpoint 4.3).
   
      3.2 Toggle audio, video, animated images. (P1)
      
    1. Allow configuration not to render audio, video, or animated image
       content, except on explicit user request. This configuration is
       required for content rendered without any user interaction
       (including content rendered on load or as the result of a script),
       as well as content rendered as the result of user interaction
       (e.g., when the user activates a link).
    2. The user agent may satisfy this checkpoint by making video and
       animated images invisible and audio silent, but this technique is
       not recommended.
    3. When configured not to render content except on explicit user
       request, the user agent is not required to retrieve the audio,
       video, or animated image from the Web until requested by the user.
       
   Techniques for checkpoint 3.2
   
   Content type labels: Animation, Video, Audio.
   
   Note: See checkpoint 2.3 for information about how to provide access
   to unrendered audio, video, and animated images. See also checkpoint
   4.5, checkpoint 4.9, and checkpoint 4.10.
   
      3.3 Toggle animated/blinking text. (P1)
      
    1. Allow configuration to render animated or blinking text content.
       as motionless, unblinking text. Blinking text is text whose visual
       rendering alternates between visible and invisible, any rate of
       change.
    2. In this configuration, the user must still have access to the same
       text content, but the user agent may render it in a separate
       viewport (e.g., for large amounts of streaming text).
    3. The user agent also satisfies this checkpoint by always rendering
       animated or blinking text as motionless, unblinking text.
       
   Techniques for checkpoint 3.3
   
   Content type labels: VisualText.
   
   Note: Animation (a rendering effect) differs from streaming (a
   delivery mechanism). Streaming content might be rendered as an
   animation (e.g., an animated stock ticker or vertically scrolling
   text) or as static text (e.g., movie subtitles, which are rendered for
   a limited time, but do not give the impression of movement). See also
   checkpoint 3.5. This checkpoint does not apply for blinking and
   animation effects that are caused by mechanisms that the user agent
   cannot recognize.
   
      3.4 Toggle scripts. (P1)
      
    1. Allow configuration not to execute any executable content (e.g.,
       scripts and applets).
    2. In this configuration, provide an option to alert the user when
       executable content is available (but has not been executed).
    3. The user agent is only required to alert the user to the presence
       of more than zero scripts or applets (i.e., per-element alerts are
       not required).
       
   Techniques for checkpoint 3.4
   
   Note: This checkpoint does not refer to plug-ins and other programs
   that are not part of content. Scripts and applets may provide very
   useful functionality, not all of which causes accessibility problems.
   Developers should not consider that the user's ability to turn off
   scripts is an effective way to improve content accessibility; turning
   off scripts means losing the benefits they offer. Instead, developers
   should provide users with finer control over user agent or content
   behavior known to raise accessibility barriers. The user should only
   have to turn off scripts as a last resort.
   
      3.5 Toggle content refresh. (P1)
      
    1. Allow configuration so that the user agent only refreshes content
       on explicit user request.
    2. In this configuration, alert the user of the refresh rate
       specified in content, and allow the user to request fresh content
       manually (e.g., by following a link or confirming a prompt).
    3. When the user chooses not to refresh content, the user agent may
       ignore that content; buffering is not required.
    4. This checkpoint only applies when the user agent (not the server)
       automatically initiates the request for fresh content.
       
   Techniques for checkpoint 3.5
   
   Note: For example, allow configuration to prompt the user to confirm
   content refresh, at the rate specified by the author.
   
      3.6 Toggle redirects. (P2)
      
    1. Allow configuration so that a "client-side redirect" (i.e., one
       initiated by the user agent, not the server) only changes content
       on explicit user request.
    2. Allow the user to access the new content on demand (e.g., by
       following a link or confirming a prompt).
    3. The user agent is not required to provide these functionalities
       for client-side redirects specified to occur instantaneously
       (i.e., after no delay).
       
   Techniques for checkpoint 3.6
   
   Note: Some HTML user agents support client-side redirects authored
   using a META element with http-equiv="refresh". Authors (and Web
   masters) should use the redirect mechanisms of HTTP instead.
   
      3.7 Toggle images. (P2)
      
    1. Allow configuration not to render image content.
    2. The user agent may satisfy this checkpoint by making images
       invisible, but this technique is not recommended.
       
   Techniques for checkpoint 3.7
   
   Content type labels: Image.
   
   Note: See checkpoint 2.3 for information about how to provide access
   to unrendered images.
   
   [next guideline 4] [review guideline 3] [previous guideline 2]
   [contents]
   
Guideline 4. Ensure user control of rendering.

    Ensure that the user can select preferred styles (colors, size of rendered
    text, synthesized speech characteristics, etc.) from choices offered by the
    user agent. Allow the user to override author-specified styles and user
    agent default styles.
    
   Providing access to content (see guideline 2) includes enabling users
   to configure and control its rendering. Users with low vision may
   require that text be rendered at a size larger than the size specified
   by the author or by the user agent's default rendering. Users with
   color blindness may need to impose or prevent certain color
   combinations.
   
   For dynamic presentations such as synchronized multimedia
   presentations created with SMIL 1.0 [SMIL], users with cognitive,
   hearing, visual, and physical disabilities may not be able to interact
   with a presentation within the time frame assumed by the author. To
   make the presentation accessible to these users, user agents rendering
   multimedia content (audio, video, and other animations), have to allow
   the user to control the playback rate of this content, and also to
   stop, start, pause, and navigate it quickly. User agents rendering
   audio have to allow the user to control the audio volume globally and
   to allow the user to control independently distinguishable audio
   tracks.
   
   User agents with speech synthesis capabilities need to allow users to
   control various synthesized speech rendering parameters. For instance,
   users who are blind and hard of hearing may not be able to make use of
   high or low frequencies; these users have to be able to configure
   their speech synthesizers to use suitable frequencies.
   
    Checkpoints for visually rendered text
    
      4.1 Configure text size. (P1)
      
    1. Allow global configuration of the reference size of visually
       rendered text, with an option to override reference sizes
       specified by the author or user agent defaults.
    2. Offer a range of text sizes to the user that includes at least:
          + the range offered by the conventional utility available in
            the operating environment that allows users to choose the
            text size (e.g., the font size),
          + or, if no such utility is available, the range of text sizes
            supported by the conventional APIs of the operating
            environment for drawing text.
       
   Techniques for checkpoint 4.1
   
   Content type labels: VisualText.
   
   Note: The reference size of rendered text corresponds to the default
   value of the CSS2 'font-size' property, which is 'medium' (refer to
   CSS2 [CSS2], section 15.2.4). For example, in HTML, this might be
   paragraph text. The default reference size of rendered text may vary
   among user agents. User agents may offer different mechanisms to allow
   control of the size of rendered text (e.g., font size control, zoom,
   magnification, etc.). Refer, for example to the Scalable Vector
   Graphics specification [SVG] for information about scalable rendering.
   
      4.2 Configure font family. (P1)
      
    1. Allow global configuration of the font family of all visually
       rendered text, with an option to override font families specified
       by the author or by user agent defaults.
    2. Offer a range of font families to the user that includes at least:
          + the range offered by the conventional utility available in
            the operating environment that allows users to choose the
            font family,
          + or, if no such utility is available, the range of font
            families supported by the conventional APIs of the operating
            environment for drawing text.
    3. For text that cannot be rendered properly using the user's
       preferred font family, the user agent may substitute an
       alternative font family.
       
   Techniques for checkpoint 4.2
   
   Content type labels: VisualText.
   
   Note: For example, allow the user to specify that all text is to be
   rendered in a particular sans-serif font family.
   
      4.3 Configure text colors. (P1)
      
    1. Allow global configuration of the foreground and background color
       of all visually rendered text, with an option to override
       foreground and background colors specified by the author or user
       agent defaults.
    2. Offer a range of colors to the user that includes at least:
          + the range offered by the conventional utility available in
            the operating environment that allows users to choose colors,
          + or, if no such utility is available, the range of colors
            supported by the conventional APIs of the operating
            environment for specifying colors.
       
   Techniques for checkpoint 4.3
   
   Content type labels: ColorText.
   
   Note: User configuration of foreground and background colors may
   inadvertently lead to the inability to distinguish ordinary text from
   selected text, focused text, etc. See checkpoint 10.3 for more
   information about highlight styles.
   
    Checkpoints for multimedia presentations and other presentations that
    change continuously over time
    
      4.4 Slow multimedia. (P1)
      
    1. Allow the user to slow the presentation rate of rendered audio and
       animations (including video and animated images).
    2. For a visual track, provide at least one setting between 40% and
       60% of the original speed.
    3. For a prerecorded audio track including audio-only presentations,
       provide at least one setting between 75% and 80% of the original
       speed.
    4. When the user agent allows the user to slow the visual track of a
       synchronized multimedia presentation to between 100% and 80% of
       its original speed, synchronize the visual and audio tracks. Below
       80%, the user agent is not required to render the audio track.
    5. The user agent is not required to satisfy this checkpoint for
       audio and animations whose recognized role is to create a purely
       stylistic effect.
       
   Techniques for checkpoint 4.4
   
   Content type labels: Animation, Audio.
   
   Note: Purely stylistic effects include background sounds, decorative
   animated images, and effects caused by style sheets. The style
   exception of this checkpoint is based on the assumption that authors
   have satisfied the requirements of the "Web Content Accessibility
   Guidelines 1.0" [WCAG10] not to convey information through style alone
   (e.g., through color alone or style sheets alone). See checkpoint 2.6
   and checkpoint 4.7.
   
      4.5 Start, stop, pause, and navigate multimedia. (P1)
      
    1. Allow the user to stop, pause, and resume rendered audio and
       animations (including video and animated images) that last three
       or more seconds at their default playback rate.
    2. Allow the user to navigate efficiently within audio and animations
       (including video and animated images) that last three or more
       seconds at their default playback rate. The user agent may satisfy
       this requirement through forward and backward sequential access
       techniques (e.g., advance three seconds), or direct access
       techniques (e.g., play starting at the 10-minute mark), or some
       combination.
    3. When serial techniques are used to satisfy the previous
       requirement, the user agent is not required to play back content
       during serial advance or rewind (though doing so may help orient
       the user).
    4. The user agent is not required to satisfy this checkpoint for
       audio and animations whose recognized role is to create a purely
       stylistic effect.
    5. When the user pauses a real-time audio or animation, the user
       agent may discard packets that continue to arrive during the
       pause.
       
   Techniques for checkpoint 4.5
   
   Content type labels: Animation, Audio.
   
   Note: See checkpoint 4.4 for more information about the exception for
   purely stylistic effects. This checkpoint applies to content that is
   either rendered automatically or on request from the user. Respect
   synchronization cues per checkpoint 2.6.
   
      4.6 Position captions. (P1)
      
    1. For graphical viewports, allow the user to position rendered
       captions with respect to synchronized visual tracks as follows:
          + if the user agent satisfies this checkpoint by using a markup
            language or style sheet language to provide configuration or
            control, then the user agent must allow the user to choose
            from among at least the range of positions enabled by the
            format
          + otherwise the user agent must allow both non-overlapping and
            overlapping positions (e.g., by rendering captions in a
            separate viewport that may be positioned on top of the visual
            track).
    2. In either case, the user agent must allow the user to override the
       author's specified position.
    3. The user agent is not required to change the layout of other
       content (i.e., reflow) after the user has changed the position of
       captions.
    4. The user agent is not required to make the captions background
       transparent when those captions are rendered above a related video
       track.
       
   Techniques for checkpoint 4.6
   
      4.7 Slow other multimedia. (P2)
      
    1. Allow the user to slow the presentation rate of rendered audio and
       animations (including video and animated images) not covered by
       checkpoint 4.4.
    2. The same speed percentage requirements of checkpoint 4.4 apply.
       
   Techniques for checkpoint 4.7
   
   Content type labels: Animation, Audio.
   
   Note: User agents automatically satisfy this checkpoint if they
   satisfy checkpoint 4.4 for all audio and animations.
   
      4.8 Control other multimedia. (P2)
      
    1. Allow the user to stop, pause, resume, and navigate efficiently
       rendered audio and animations (including video and animated
       images) not covered by checkpoint 4.5.
       
   Techniques for checkpoint 4.8
   
   Content type labels: Animation, Audio.
   
   Note: User agents automatically satisfy this checkpoint if they
   satisfy checkpoint 4.5 for all audio and animations.
   
    Checkpoints for audio volume control
    
      4.9 Global volume control. (P1)
      
    1. Allow global configuration of the volume of all rendered audio,
       with an option to override audio volumes specified by the author
       or user agent defaults.
    2. Allow the user to choose zero volume (i.e., silent).
       
   Techniques for checkpoint 4.9
   
   Content type labels: Audio.
   
   Note: User agents should allow configuration of volume through
   available operating environment controls.
   
      4.10 Independent volume control. (P1)
      
    1. Allow independent control of the volumes of rendered audio sources
       synchronized to play simultaneously.
    2. The user agent is not required to satisfy this checkpoint for
       audio whose recognized role is to create a purely stylistic
       effect.
    3. The user control required by this checkpoint includes the ability
       to override author-specified volumes for the relevant sources of
       audio.
       
   Techniques for checkpoint 4.10
   
   Content type labels: Audio.
   
   Note: See checkpoint 4.4 for more information about the exception for
   purely stylistic effects. The user agent should satisfy this
   checkpoint by allowing the user to control independently the volumes
   of all audio sources (e.g., by implementing a general audio mixer type
   of functionality). See also checkpoint 4.13.
   
      4.11 Control other volume. (P2)
      
    1. Allow independent control of the volumes of rendered audio sources
       synchronized to play simultaneously that are not covered by
       checkpoint 4.10.
       
   Techniques for checkpoint 4.11
   
   Content type labels: Audio.
   
   Note: User agents automatically satisfy this checkpoint if they
   satisfy checkpoint 4.10 for all audio.
   
    Checkpoints for synthesized speech rendering
    
      4.12 Configure synthesized speech rate. (P1)
      
    1. Allow configuration of the synthesized speech rate, according to
       the full range offered by the speech synthesizer.
       
   Techniques for checkpoint 4.12
   
   Content type labels: Speech.
   
   Note: The range of synthesized speech rates offered by the speech
   synthesizer may depend on natural language.
   
      4.13 Configure synthesized speech volume. (P1)
      
    1. Allow control of the synthesized speech volume, independent of
       other sources of audio.
    2. The user control required by this checkpoint includes the ability
       to override author-specified synthesized speech volume.
       
   Techniques for checkpoint 4.13
   
   Content type labels: Speech.
   
   Note: See also checkpoint 4.10.
   
      4.14 Configure synthesized speech characteristics. (P1)
      
    1. Allow configuration of synthesized speech characteristics
       according to the full range of values offered by the speech
       synthesizer.
       
   Techniques for checkpoint 4.14
   
   Note: Some speech synthesizers allow users to choose values for
   synthesized speech characteristics at a higher abstraction layer,
   i.e., by choosing from present options that group several
   characteristics. Some typical options one might encounter include:
   "adult male voice", "female child voice", "robot voice", "pitch",
   "stress", etc. Ranges for values may vary among speech synthesizers.
   
      4.15 Specific synthesized speech characteristics. (P2)
      
    1. Allow configuration of the following synthesized speech
       characteristics: pitch, pitch range, stress, richness.
    2. Pitch refers to the average frequency of the speaking voice.
    3. Pitch range specifies a variation in average frequency.
    4. Stress refers to the height of "local peaks" in the intonation
       contour of the voice.
    5. Richness refers to the richness or brightness of the voice.
       
   Techniques for checkpoint 4.15
   
   Note: This checkpoint is more specific than checkpoint 4.14: it
   requires support for the voice characteristics listed. Definitions for
   these characteristics are based on descriptions in section 19 of the
   Cascading Style Sheets Level 2 Recommendation [CSS2]; please refer to
   that specification for additional informative descriptions. Some
   speech synthesizers allow users to choose values for synthesized
   speech characteristics at a higher abstraction layer, i.e., by
   choosing from present options distinguished by "gender", "age",
   "accent", etc. Ranges of values may vary among speech synthesizers.
   
   Content type labels: Speech.
   
      4.16 Configure synthesized speech features. (P2)
      
    1. Provide support for user-defined extensions to the synthesized
       speech dictionary, as well as the following functionalities:
          + spell-out: spell text one character at a time or according to
            language-dependent pronunciation rules;
          + speak-numeral: speak a numeral as individual digits or as a
            full number; and
          + speak-punctuation: speak punctuation literally or render as
            natural pauses.
       
   Techniques for checkpoint 4.16
   
   Note: Definitions for the functionalities listed are based on
   descriptions in section 19 of the Cascading Style Sheets Level 2
   Recommendation [CSS2]; please refer to that specification for
   additional informative descriptions.
   
    Checkpoints related to style sheets
    
      4.17 Choose style sheets. (P1)
      
    1. For user agents that support style sheets:
          + Allow the user to choose from and apply available author
            style sheets (in content).
          + Allow the user to choose from and apply available user style
            sheets.
          + Allow the user to ignore author and user style sheets.
       
   Techniques for checkpoint 4.17
   
   Note: By definition, the user agent's default style sheet is always
   present, but may be overridden by author or user styles. Developers
   should not consider that the user's ability to turn off author and
   user style sheets is an effective way to improve content
   accessibility; turning off style sheet support means losing the many
   benefits they offer. Instead, developers should provide users with
   finer control over user agent or content behavior known to raise
   accessibility barriers. The user should only have to turn off author
   and user style sheets as a last resort.
   
   [next guideline 5] [review guideline 4] [previous guideline 3]
   [contents]
   
Guideline 5. Ensure user control of user interface behavior.

    Ensure that the user can control the behavior of viewports and other user
    interface controls, including those that may be manipulated by the author
    (e.g., through scripts).
    
   Control of viewport behavior is important to accessibility. For people
   with visual disabilities or certain types of learning disabilities, it
   is important that the point of regard - what the user is presumed to
   be viewing - remain as stable as possible. Unexpected changes may
   cause users to lose track of how many viewports are open, which
   viewport has the current focus, etc. This guideline includes
   requirements for control of opening and closing viewports, the
   relative position of graphical viewports, changes to focus, and
   inadvertent form submissions and micropayments.
   
    Checkpoints
    
      5.1 No automatic content focus change. (P2)
      
    1. Allow configuration so that if a viewport opens without explicit
       user request, its content focus does not automatically become the
       current focus.
    2. Configuration is preferred, but is not required if the content
       focus can only ever be moved on explicit user request.
       
   Techniques for checkpoint 5.1
   
      5.2 Keep viewport on top. (P2)
      
    1. For graphical user interfaces, allow configuration so that the
       viewport with the current focus remains "on top" of all other
       viewports with which it overlaps.
       
   Techniques for checkpoint 5.2
   
      5.3 Manual viewport open only. (P2)
      
    1. Allow configuration so that viewports only open on explicit user
       request.
    2. In this configuration, instead of opening a viewport
       automatically, alert the user and allow the user to open it on
       demand (e.g., by following a link or confirming a prompt).
    3. Allow the user to close viewports.
    4. If a viewport (e.g., a frame set) contains other viewports, these
       requirements only apply to the outermost container viewport.
    5. Configuration is preferred, but is not required if viewports can
       only ever open on explicit user request.
    6. User creation of a new viewport (e.g., empty or with a new
       resource loaded) through the user agent's user interface
       constitutes an explicit user request.
       
   Techniques for checkpoint 5.3
   
   Note: Generally, viewports open automatically as the result of
   instructions in content. See also checkpoint 5.1 (for control over
   changes of focus when a viewport opens) and checkpoint 6.5 (for
   programmatic alert of changes to the user interface).
   
      5.4 Selection and focus in viewport. (P2)
      
    1. Ensure that when a viewport's selection or content focus changes,
       it is at least partially in the viewport after the change.
       
   Techniques for checkpoint 5.4
   
   Note: For example, if users navigating links move to a portion of the
   document outside a graphical viewport, the viewport should scroll to
   include the new location of the focus. Or, for users of audio
   viewports, allow configuration to render the selection or focus
   immediately after the change.
   
      5.5 Confirm form submission. (P2)
      
    1. Allow configuration to prompt the user to confirm (or cancel) any
       form submission.
    2. Configuration is preferred, but it not required if forms can only
       ever be submitted on explicit user request.
       
   Techniques for checkpoint 5.5
   
   Note: For example, do not submit a form automatically when a menu
   option is selected, when all fields of a form have been filled out, or
   when a "mouseover" or "change" event occurs.
   
      5.6 Confirm fee links. (P2)
      
    1. Allow configuration to prompt the user to confirm (or cancel) any
       payment that results from activation of a fee link.
    2. Configuration is preferred, but is not required if fee links can
       only ever be activated on explicit user request.
       
   Techniques for checkpoint 5.6
   
      5.7 Manual viewport close only. (P3)
      
    1. Allow configuration to prompt the user to confirm (or cancel)
       closing any viewport that starts to close without explicit user
       request.
       
   Techniques for checkpoint 5.7
   
   [next guideline 6] [review guideline 5] [previous guideline 4]
   [contents]
   
Guideline 6. Implement interoperable application programming interfaces.

    Implement interoperable interfaces to communicate with other software
    (e.g., assistive technologies, the operating environment, plug-ins, etc.).
    
   This guideline addresses interoperability between a conforming user
   agent and other software, in particular assistive technologies. The
   checkpoints of this guideline require implementation of application
   programming interfaces (APIs) for communication. There are three types
   of requirements in this guideline:
    1. Requirements for what information must be communicated through an
       API.
    2. Requirements for which APIs or types of APIs must be used to
       communicate this information.
    3. Requirements for additional characteristics of these APIs.
       
   Note: The User Agent Accessibility Guidelines Working Group believes
   that, in order to promote interoperability between a conforming user
   agent and more than one assistive technology, it is more important to
   implement conventional APIs than custom APIs, even though custom APIs
   may superior access. When conventional APIs do not allow users to
   satisfy the requirements of these checkpoints, however, developers may
   implement alternative APIs in order to conform to this document.
   
    Checkpoints
    
      6.1 DOM read access. (P1)
      
    1. Provide programmatic read access to HTML and XML content by
       conforming to the following modules of the W3C Document Object
       Model DOM Level 2 Core Specification [DOM2CORE] and exporting the
       interfaces they define:
          + the Core module for HTML;
          + the Core and XML modules for XML.
       
   Techniques for checkpoint 6.1
   
   Note: Please refer to the "Document Object Model (DOM) Level 2 Core
   Specification" [DOM2CORE] for information about HTML and XML versions
   covered.
   
      6.2 DOM write access. (P1)
      
    1. If the user can modify HTML and XML content through the user
       interface, provide the same functionality programmatically by
       conforming to the following modules of the W3C Document Object
       Model DOM Level 2 Core Specification [DOM2CORE] and exporting the
       interfaces they define:
          + the Core module for HTML;
          + the Core and XML modules for XML.
       
   Techniques for checkpoint 6.2
   
   Note: For example, if the user interface allows users to complete HTML
   forms, this must also be possible through the required DOM APIs.
   Please refer to the "Document Object Model (DOM) Level 2 Core
   Specification" [DOM2CORE] for information about HTML and XML versions
   covered.
   
      6.3 Programmatic access to non-HTML/XML content. (P1)
      
    1. For markup languages other than HTML and XML, provide programmatic
       read access to content.
    2. Provide programmatic write access for those parts of content that
       the user can modify through the user interface. To satisfy these
       requirements, implement at least one API that is either
          + defined by a W3C Recommendation, or
          + a publicly documented API designed to enable interoperability
            with assistive technologies.
    3. If no such API is available, or if available APIs do not enable
       the user agent to satisfy the requirements, implement at least one
       publicly documented API to satisfy the requirements, and follow
       operating environment conventions for the use of input and output
       APIs.
    4. An API is considered available if the specification of the API is
       published (e.g., as a W3C Recommendation) in time for integration
       into a user agent's development cycle.
       
   Techniques for checkpoint 6.3
   
   Note: This checkpoint addresses content not covered by checkpoints
   checkpoint 6.1 and checkpoint 6.2.
   
      6.4 Programmatic operation. (P1)
      
    1. Provide programmatic read access to user agent user interface
       controls.
    2. Provide programmatic write access for those controls that the user
       can modify through the user interface. For security reasons, user
       agents are not required to allow instructions in content to modify
       user agent user interface controls.
    3. To satisfy these requirements, implement at least one API that is
       either
          + defined by a W3C Recommendation, or
          + a publicly documented API designed to enable interoperability
            with assistive technologies.
    4. If no such API is available, or if available APIs do not enable
       the user agent to satisfy the requirements, implement at least one
       publicly documented API that allows programmatic operation of all
       of the functionalities that are available through the user agent
       user interface, and follow operating environment conventions for
       the use of input and output APIs.
    5. An API is considered available if the specification of the API is
       published (e.g., as a W3C Recommendation) in time for integration
       into a user agent's development cycle.
       
   For user agent features. Techniques for checkpoint 6.4
   
   Note: APIs used to satisfy the requirements of this checkpoint may be
   platform-independent APIs such as the W3C DOM, conventional APIs for a
   particular operating environment, conventional APIs for programming
   languages, plug-ins, virtual machine environments, etc. User agent
   developers are encouraged to implement APIs that allow assistive
   technologies to interoperate with multiple types of software in a
   given operating environment (user agents, word processors, spreadsheet
   programs, etc.), as this reuse will benefit users and assistive
   technology developers. User agents should always follow operating
   environment conventions for the use of input and output APIs.
   
      6.5 Programmatic alert of changes. (P1)
      
    1. Provide programmatic alert of changes to content, user interface
       controls, selection, content focus, and user interface focus.
    2. To satisfy these requirements, implement at least one API that is
       either
          + defined by a W3C Recommendation, or
          + a publicly documented API designed to enable interoperability
            with assistive technologies.
    3. If no such API is available, or if available APIs do not enable
       the user agent to satisfy the requirements, implement at least one
       publicly documented API to satisfy the requirements, and follow
       operating environment conventions for the use of input and output
       APIs.
    4. An API is considered available if the specification of the API is
       published (e.g., as a W3C Recommendation) in time for integration
       into a user agent's development cycle.
       
   For both content and user agent. Techniques for checkpoint 6.5
   
   Note: For instance, when user interaction in one frame causes
   automatic changes to content in another, provide a programmatic alert.
   This checkpoint does not require the user agent to alert the user of
   rendering changes caused by content (e.g., an animation effect or an
   effect caused by a style sheet), just changes to the content itself.
   
      6.6 Conventional keyboard APIs. (P1)
      
    1. Follow operating environment conventions when implementing APIs
       for the keyboard.
    2. If such APIs for the keyboard do not exist, implement publicly
       documented APIs for the keyboard.
       
   Techniques for checkpoint 6.6
   
   Note: An operating environment may define more than one conventional
   API for the keyboard. For instance, for Japanese and Chinese, input
   may be processed in two stages, with an API for each.
   
      6.7 API character encodings. (P1)
      
    1. For an API implemented to satisfy requirements of this document,
       support the character encodings required for that API.
       
   For both content and user agent. Techniques for checkpoint 6.7
   
   Note: Support for character encodings is important so that text is not
   "broken" when communicated to assistive technologies. For example, the
   DOM Level 2 Core Specification [DOM2CORE], section 1.1.5 requires that
   the DOMString type be encoded using UTF-16. This checkpoint is an
   important special case of the other API requirements of this document.
   
      6.8 DOM CSS access. (P2)
      
    1. For user agents that implement Cascading Style Sheets (CSS),
       provide programmatic access to those style sheets in content by
       conforming to the CSS module of the W3C Document Object Model
       (DOM) Level 2 Style Specification [DOM2STYLE] and exporting the
       interfaces it defines.
    2. For the purposes of satisfying this checkpoint, Cascading Style
       Sheets (CSS) are defined by either CSS Level 1 [CSS1] or CSS Level
       2 [CSS2].
       
   Techniques for checkpoint 6.8
   
   Note: Please refer to the "Document Object Model (DOM) Level 2 Style
   Specification" [DOM2STYLE] for information about CSS versions covered.
   
      6.9 Timely access. (P2)
      
    1. Ensure that programmatic exchanges proceed in a timely manner.
       
   For both content and user agent. Techniques for checkpoint 6.9
   
   Note: For example, the programmatic exchange of information required
   by other checkpoints in this document should be efficient enough to
   prevent information loss, a risk when changes to content or user
   interface occur more quickly than the communication of those changes.
   Timely exchange is also important for the proper synchronization of
   alternative renderings. The techniques for this checkpoint explain how
   developers can reduce communication delays. This will help ensure that
   assistive technologies have timely access to the document object model
   and other information that is important for providing access.
   
   [next guideline 7] [review guideline 6] [previous guideline 5]
   [contents]
   
Guideline 7. Observe operating environment conventions.

    Observe operating environment conventions for the user agent user
    interface, documentation, installation, etc.
    
   Part of user agent accessibility involves following the conventions of
   the user's operating environment. This includes:
     * following operating environment conventions for user agent user
       interface design, documentation, and installation.
     * incorporating operating environment-level user preferences into
       the user agent. For instance, some operating systems include
       settings that allow users to request high-contrast colors (for
       users with low vision) or graphical rendering of audio cues (for
       users with hearing disabilities).
       
   Following operating environment conventions increases predictability
   for users and for developers of assistive technologies. Platform
   guidelines explain what users will expect from the look and feel of
   the user interface, keyboard conventions, documentation, etc. Platform
   guidelines also include information about accessibility features that
   the user agent should adopt rather than reimplement.
   
    Checkpoints
    
      7.1 Focus and selection conventions. (P1)
      
    1. Follow operating environment conventions that benefit
       accessibility when implementing the selection, content focus, and
       user interface focus.
       
   Techniques for checkpoint 7.1
   
   Note: This checkpoint is an important special case of checkpoint 7.3.
   See also checkpoint 9.1 and checkpoint 9.2.
   
      7.2 Respect input configuration conventions. (P1)
      
    1. Ensure that default input configurations of the user agent do not
       interfere with operating environment accessibility conventions
       (e.g., for keyboard accessibility).
       
   For user agent features. Techniques for checkpoint 7.2
   
   Note: Information about operating environment accessibility
   conventions is available in the Techniques document [UAAG10-TECHS].
   See also checkpoint 11.5.
   
      7.3 Operating environment conventions. (P2)
      
    1. Follow operating environment conventions that benefit
       accessibility. In particular, follow conventions that benefit
       accessibility for user interface design, keyboard configuration,
       product installation, and documentation.
    2. For the purposes of this checkpoint, an operating environment
       convention that benefits accessibility is either
          + one identified as such in operating environment design or
            accessibility guidelines, or
          + one that allows the author to satisfy any requirement of the
            "Web Content Accessibility Guidelines 1.0" [WCAG10] or of the
            current document.
       
   For user agent features. Techniques for checkpoint 7.3
   
   Note: Some of these conventions (e.g., sticky keys, mouse keys, show
   sounds, etc.) are discussed in the Techniques document [UAAG10-TECHS].
   
      7.4 Input configuration indications. (P2)
      
    1. Follow operating environment conventions to indicate the input
       configuration.
       
   For user agent features. Techniques for checkpoint 7.4
   
   Note: For example, in some operating environments, when a
   functionality may be triggered through a menu and through the
   keyboard, the developer may design the menu entry so that the
   character of the activating key is also shown. This checkpoint is an
   important special case of checkpoint 7.3. See also checkpoint 11.5.
   
   [next guideline 8] [review guideline 7] [previous guideline 6]
   [contents]
   
Guideline 8. Implement specifications that benefit accessibility.

    Support the accessibility features of all implemented specifications.
    Implement W3C Recommendations when available and appropriate for a task.
    
   Developers should implement open specifications. Conformance to open
   specifications benefits interoperability and accessibility by making
   it easier to design assistive technologies (also discussed in
   guideline 6).
   
   While developers should implement the accessibility features of any
   specification (checkpoint 8.1), this document recommends conformance
   to W3C Recommendations in particular (checkpoint 8.2) for several
   reasons:
     * W3C specifications include "built-in" accessibility features.
     * W3C specifications undergo early review to ensure that
       accessibility issues are considered during the design phase. This
       review includes review from stakeholders in accessibility.
     * W3C specifications are developed in a consensus process (refer to
       the process defined by the W3C Process Document [W3CPROCESS]). W3C
       encourages the public to review and comment on these
       specifications (public Working Drafts, Candidate Recommendations,
       and Proposed Recommendations). For information about how
       specifications become W3C Recommendations, refer to the W3C
       Recommendation track ([W3CPROCESS], section 6.2). W3C
       Recommendations (and other technical reports) are published at the
       W3C Web site.
       
    Checkpoints
    
      8.1 Implement accessibility features. (P1)
      
    1. Implement the accessibility features of specifications (markup
       languages, style sheet languages, metadata languages, graphics
       formats, etc.). For the purposes of this checkpoint, an
       accessibility feature is either
          + one identified as such, or
          + one that allows the author to satisfy any requirement of the
            "Web Content Accessibility Guidelines 1.0" [WCAG10].
       
   For all content. Techniques for checkpoint 8.1
   
   Note: This checkpoint applies to both W3C-developed and non-W3C
   specifications. The Techniques document [UAAG10-TECHS] provides
   information about the accessibility features of some specifications,
   including W3C specifications. The user agent is not required to
   satisfy this checkpoint for all implemented specifications; see the
   section on conformance and implementing specifications for more
   information.
   
      8.2 Conform to specifications. (P2)
      
    1. Use and conform to either
          + W3C Recommendations when they are available and appropriate
            for a task, or
          + non-W3C specifications that enable the creation of content
            that conforms at level A or better to the Web Content
            Accessibility Guidelines 1.0 [WCAG10].
    2. When a requirement of another specification contradicts a
       requirement of the current document, the user agent may disregard
       the requirement of the other specification and still satisfy this
       checkpoint.
    3. A specification is considered available if it is published (e.g.,
       as a W3C Recommendation) in time for integration into a user
       agent's development cycle.
       
   For all content. Techniques for checkpoint 8.2
   
   Note: For instance, for markup, the user agent may conform to HTML 4
   [HTML4], XHTML 1.0 [XHTML10], or XML 1.0 [XML]. For style sheets, the
   user agent may conform to CSS ([CSS1], [CSS2]). For mathematics, the
   user agent may conform to MathML 2.0 [MATHML20]. For synchronized
   multimedia, the user agent may conform to SMIL 1.0 [SMIL]. The user
   agent is not required to satisfy this checkpoint for all implemented
   specifications; see the section on conformance and implementing
   specifications for more information.
   
   [next guideline 9] [review guideline 8] [previous guideline 7]
   [contents]
   
Guideline 9. Provide navigation mechanisms.

    Provide access to content through a variety of navigation mechanisms:
    sequential navigation, direct navigation, searches, structured navigation,
    etc.
    
   Users should be able to navigate to important pieces of content within
   a configurable view, identify the type of object they have navigated
   to, interact with that object easily (if it is an enabled element),
   and review the surrounding context (to orient themselves). Providing a
   variety of navigation and search mechanisms helps users with
   disabilities (and all users) access content more efficiently.
   Navigation and searching are particularly important to users who
   access content serially (e.g., as synthesized speech or braille).
   
   Sequential navigation (e.g., line scrolling, page scrolling,
   sequential navigation through enabled elements, etc.) means advancing
   (or rewinding) through rendered content in well-defined steps (line by
   line, screen by screen, link by link, etc.). Sequential navigation can
   provide context, but can be time-consuming. Sequential navigation is
   important to users who cannot scan a page visually for context and
   also benefits users unfamiliar with a page. Sequential access may be
   based on element type (e.g., links only), content structure (e.g.,
   navigation from heading to heading), or other criteria.
   
   Direct navigation (e.g., to a particular link or paragraph) is faster
   than sequential navigation, but generally requires familiarity with
   the content. Direct navigation is important to users with some
   physical disabilities (who may have little or no manual dexterity
   and/or increased tendency to push unwanted buttons or keys), to users
   with visual disabilities, and also benefits "power users." Direct
   navigation may be possible with the pointing device or the keyboard
   (e.g., keyboard shortcuts).
   
   Structured navigation mechanisms offer both context and speed. User
   agents should allow users to navigate to content known to be
   structurally important: blocks of content, headers and sections,
   tables, forms and form elements, enabled elements, navigation
   mechanisms, containers, etc. For information about programmatic access
   to document structure, see guideline 6.
   
   User agents should allow users to configure navigation mechanisms
   (e.g., to allow navigation of links only, or links and headings, or
   tables and forms, etc.).
   
    Checkpoints
    
      9.1 Provide content focus. (P1)
      
    1. Provide at least one content focus for each viewport (including
       frames) where enabled elements are part of the rendered content.
    2. Allow the user to make the content focus of each viewport the
       current focus.
       
   Techniques for checkpoint 9.1
   
   Note: For example, when two frames of a frameset contain enabled
   elements, allow the user to make the content focus of either frame the
   current focus. Note that viewports "owned" by plug-ins that are part
   of a conformance claim are also covered by this checkpoint.
   
      9.2 Provide user interface focus. (P1)
      
    1. Provide a user interface focus.
       
   Techniques for checkpoint 9.2
   
      9.3 Move content focus. (P1)
      
    1. Allow the user to move the content focus to any enabled element in
       the viewport.
    2. Allow configuration so that the content focus of a viewport only
       changes on explicit user request. Configuration is not required if
       the content focus only ever changes on explicit user request. See
       also checkpoint 5.1.
    3. If the author has not specified a navigation order, allow at least
       forward sequential navigation to each element, in document order.
    4. The user agent may also include disabled elements in the
       navigation order.
       
   Techniques for checkpoint 9.3
   
   Note: In addition to forward sequential navigation, the user agent
   should also allow reverse sequential navigation. This checkpoint is an
   important special case of checkpoint 9.9.
   
      9.4 Restore history. (P1)
      
    1. For user agents that implement a viewport history mechanism, for
       each state in a viewport's browsing history, maintain information
       about the point of regard, content focus, and selection.
    2. When the user returns to any state in the viewport history,
       restore the saved values for these three state variables.
       
   Techniques for checkpoint 9.4
   
   Note: For example, when the user uses the "back button", restore the
   point of regard, content focus, and selection for previous state in
   the viewport's history.
   
      9.5 No events on focus change. (P2)
      
    1. Allow configuration so that moving the content focus to or from an
       enabled element does not automatically activate any explicitly
       associated event handlers.
       
   Techniques for checkpoint 9.5
   
   Note: For instance, in this configuration for an HTML document, do not
   activate any handlers for the 'onfocus', 'onblur', or 'onchange'
   attributes. In this configuration, user agents should still apply any
   stylistic changes (e.g., highlighting) that may occur when there is a
   change in content focus.
   
      9.6 Show event handlers. (P2)
      
    1. For the element with content focus, make available the list of
       input device event handlers explicitly associated with the
       element.
       
   Techniques for checkpoint 9.6
   
   Note: For example, allow the user to query the element with content
   focus for the list of input device event handlers, or add them
   directly to the serial navigation order described in checkpoint 9.3.
   See checkpoint 1.2 for information about activation of event handlers
   associated with the element with focus.
   
      9.7 Move content focus optimally. (P2)
      
    1. Allow the user to move the content focus to any enabled element in
       the viewport.
    2. If the author has not specified a navigation order, allow at least
       forward and reverse sequential navigation to each element, in
       document order.
    3. The user agent must not include disabled elements in the
       navigation order.
       
   Techniques for checkpoint 9.7
   
   Note: This checkpoint is a special case of checkpoint 9.3.
   
      9.8 Text search. (P2)
      
    1. Allow the user to search within rendered text for a sequence of
       characters from the document character set.
    2. Allow the user to start a forward search (in document order) from
       any selected or focused location in content.
    3. When there is a match do both of the following:
          + move the viewport so that the matched text content is within
            it, and
          + allow the user to search for the next instance of the text
            from the location of the match.
    4. Alert the user when there is no match, when the search reaches the
       end of content, and prior to any wrapping. A wrapping search is
       one that restarts automatically at the beginning of content once
       the end of content has been reached.
    5. Provide a case-insensitive search option for text in scripts
       (i.e., writing systems) where case is significant.
       
   For all rendered content. Techniques for checkpoint 9.8
   
   Note: If the user has not indicated a start position for the search,
   the search should start from the beginning of content. Per checkpoint
   7.3, use operating environments conventions for indicating the result
   of a search (e.g., selection or content focus).
   
      9.9 Structured navigation. (P2)
      
    1. Allow the user to navigate efficiently to and among important
       structural elements in rendered content.
    2. Allow forward and backward sequential navigation to these
       important structural elements.
       
   Techniques for checkpoint 9.9
   
   Note: This specification intentionally does not identify which
   "important elements" must be navigable as this will vary according to
   markup language. What constitutes "efficient navigation" may depend on
   a number of factors as well, including the "shape" of content (e.g.,
   serial navigation of long lists is not efficient) and desired
   granularity (e.g., among tables, then among the cells of a given
   table). Refer to the Techniques document [UAAG10-TECHS] for
   information about identifying and navigating important elements.
   
      9.10 Configure important elements. (P3)
      
    1. Allow configuration of the set of important elements required by
       checkpoint 9.9 and checkpoint 10.5.
    2. Allow the user to include and exclude element types in the set of
       elements.
       
   Techniques for checkpoint 9.10
   
   Note: For example, allow the user to navigate only paragraphs, or only
   headings and paragraphs, or to suppress and restore navigation bars,
   to navigate within and among tables and table cells, etc.
   
   [next guideline 10] [review guideline 9] [previous guideline 8]
   [contents]
   
Guideline 10. Orient the user.

    Provide information that will help the user understand browsing context.
    
   All users require clues to help them understand their "location" when
   browsing: where they are, how they got there, where they can go,
   what's nearby, etc. Some mechanisms that provide such clues through
   the user interface (visually, as audio, or as braille) include:
     * information about the current state of the user's interaction with
       content: where the viewport is in content (shown, for example,
       through proportional scroll bars), which viewport has the current
       focus, where the user has selected content, a history mechanism,
       the title of the current document or frame, etc. These clues need
       to be available to the user in a device-independent manner;
     * information about specific elements, such as the dimensions of a
       table, the length of an audio clip, the structure of a form,
       whether following a link will involve a fee, etc.
     * information about relationships among elements, such as between
       table cells and related table headers.
     * information about the structure of content. For instance, a
       navigable outline view can accelerate access to content while
       preserving context.
       
   Orientation mechanisms such as these are especially important to users
   who view content serially, (e.g., when rendered as synthesized speech
   or braille). For instance, these users cannot "scan" a graphically
   displayed table with their eyes for information about a table cell's
   headers, neighboring cells, etc. User agents need to provide other
   means for users to understand table cell relationships, frame
   relationships (what relationship does the graphical layout convey?),
   form context (have I filled out the form completely?), link
   information (have I already visited this link?), etc.
   
   This guideline also includes requirements to allow the user to control
   some user agent behavior (form submission and activation of fee links)
   that, if carried out automatically, might go unnoticed by some users
   (e.g., users with blindness) or might disorient others (e.g., some
   users with a cognitive disability).
   
    Checkpoints
    
      10.1 Table orientation. (P1)
      
    1. Make available to the user the purpose of each rendered table
       (e.g., as expressed in a summary or table caption) and the
       relationships among the table cells and headers.
       
   Techniques for checkpoint 10.1
   
   Note: This checkpoint refers only to table purpose and cell/header
   relationship information that the user agent can recognize. Depending
   on the table, some techniques may be more efficient than others for
   conveying data relationships. For many tables, user agents rendering
   in two dimensions may satisfy this checkpoint by rendering a table as
   a grid and by ensuring that users can find headers associated with
   cells. However, for large tables or small viewports, allowing the user
   to query cells for information about related headers may improve
   access. This checkpoint is an important special case of checkpoint
   2.1.
   
      10.2 Highlight selection and content focus. (P1)
      
    1. Provide a mechanism for highlighting the selection and content
       focus of each viewport.
    2. The highlight mechanism must not rely on color alone.
    3. Allow global configuration of selection and focus highlight
       styles.
    4. For graphical viewports, if the highlight mechanism involves
       colors or text decorations, offer a range of colors or text
       decorations to the user that includes at least:
          + the range offered by the conventional utility available in
            the operating environment that allows users to choose colors
            or text decorations,
          + or, if no such utility is available, the range of colors or
            text decorations supported by the conventional APIs of the
            operating environment for specifying colors or drawing text.
       
   Techniques for checkpoint 10.2
   
   Note: Examples of highlight mechanisms include foreground and
   background color variations, underlining, distinctive synthesized
   speech prosody, border styling, etc. Because the selection and focus
   change frequently, user agents should not highlight them using
   mechanisms (e.g., font size variations) that cause content to reflow
   as this may disorient the user. See also checkpoint 7.1.
   
      10.3 Distinct default highlight styles. (P1)
      
    1. Ensure that all of the default highlight styles for the selection
       and content focus, as well as for enabled elements, recently
       visited links, and fee links in rendered content:
          + do not rely on color alone, and
          + differ from each other, and not by color alone.
    2. This checkpoint does not apply to those highlight styles inherited
       from the operating environment as default values, as long as the
       user can change the styles in the operating environment.
       
   Techniques for checkpoint 10.3
   
   Note: For instance, by default a graphical user agent may present the
   selection using color and a dotted outline, the focus using a solid
   outline, enabled elements as underlined in blue, recently visited
   links as dotted underlined in purple, and fee links using a special
   icon or flag to draw the user's attention.
   
      10.4 Highlight special elements. (P2)
      
    1. Provide a mechanism for highlighting all enabled elements,
       recently visited links, and fee links in rendered content.
    2. Allow the user to configure the highlight styles. The highlight
       mechanism must not rely on color alone.
    3. For graphical viewports, if the highlight mechanism involves text
       size, font family, colors, or text decorations, offer the
       corresponding range of values required by checkpoint 4.1,
       checkpoint 4.2, checkpoint 4.3, or checkpoint 10.2.
    4. For a graphically rendered enabled elements, highlight the most
       specific rendered element that:
          + encompasses the enabled element, and
          + is rendered as a coherent unit according to specification.
       For example, an HTML user agent rendering a PNG image as part of
       an image map is only required to highlight the image as a whole,
       not each enabled region. On the other hand, an SVG user agent
       rendering an SVG image with embedded graphical links is required
       to highlight each graphical link that may be rendered
       independently according to the SVG specification.
       
   Techniques for checkpoint 10.4
   
   Note: Examples of highlight mechanisms include foreground and
   background color variations, font variations, underlining, distinctive
   synthesized speech prosody, border styling, etc.
   
      10.5 Outline view. (P2)
      
    1. Make available to the user an "outline" view of content, composed
       of labels for important structural elements (e.g., heading text,
       table titles, form titles, etc.).
    2. What constitutes a label is defined by each markup language
       specification. A label is not required to be text only.
       
   Techniques for checkpoint 10.5
   
   Note: This checkpoint is meant to provide the user with a simplified
   view of content (e.g, a table of contents). For example, in HTML, a
   heading (H1-H6) is a label for the section that follows it, a CAPTION
   is a label for a table, the "title" attribute is a label for its
   element, etc. For important elements that do not have associated
   labels, user agents may generate labels for the outline view. For
   information about what constitutes the set of important structural
   elements, please see the Note following checkpoint 9.9. By making the
   outline view navigable, it is possible to satisfy this checkpoint and
   checkpoint 9.9 together: allow users to navigate among the important
   elements of the outline view, and to navigate from a position in the
   outline view to the corresponding position in a full view of content.
   See also checkpoint 9.10.
   
      10.6 Provide link information. (P3)
      
    1. To help the user decide whether to traverse a link, make available
       the following information about it:
          + link element content,
          + link title,
          + whether the link is internal to the resource (e.g., the link
            is to a target in the same Web page),
          + whether the user has traversed the link recently,
          + whether traversing it may involve a fee, and
          + information about the type, size, and natural language of
            linked Web resources.
    2. The user agent is not required to compute or make available
       information that requires retrieval of linked Web resources.
       
   Techniques for checkpoint 10.6
   
    Checkpoints for the user interface
    
      10.7 Highlight current viewport. (P1)
      
    1. Provide a mechanism for highlighting the viewport with the current
       focus (including any frame that takes current focus).
    2. For graphical viewports, the default highlight mechanism must not
       rely on color alone.
    3. This default color requirement does not apply if the highlight
       mechanism is inherited from the operating environment as the
       default and the user can change it in the operating environment.
       
   Techniques for checkpoint 10.7
   
   Note: This checkpoint is an important special case of checkpoint 1.1.
   See also to checkpoint checkpoint 7.1.
   
      10.8 Indicate rendering progress. (P3)
      
    1. Indicate the viewport's position relative to rendered content
       (e.g., the proportion of an audio or video clip that has been
       played, the proportion of a Web page that has been viewed, etc.).
    2. The user agent may calculate the relative position according to
       content focus position, selection position, or viewport position,
       depending on how the user has been browsing.
    3. For two-dimensional renderings, relative position includes both
       vertical and horizontal positions.
    4. The user agent may indicate the proportion of content viewed in a
       number of ways, including as a percentage, as a relative size in
       bytes, etc.
       
   Techniques for checkpoint 10.8
   
   [next guideline 11] [review guideline 10] [previous guideline 9]
   [contents]
   
Guideline 11. Allow configuration and customization.

    Allow users to configure the user agent so that frequently performed tasks
    are made convenient, and allow users to save their preferences.
    
   Web users have a wide range of capabilities and need to be able to
   configure the user agent according to their preferences for styles,
   graphical user interface configuration, keyboard configuration, etc.
   Most of the checkpoints in this guideline pertain to the input
   configuration: how user agent behavior is controlled through keyboard
   input, pointing device input, and voice input.
   
    Checkpoints
    
      11.1 Current user bindings. (P1)
      
    1. Provide information to the user about current user preferences for
       input configurations.
    2. To satisfy this checkpoint, the user agent may make available
       binding information in a centralized fashion (e.g., a list of
       bindings) or a distributed fashion (e.g., by listing keyboard
       shortcuts in user interface menus).
       
   For user agent features. Techniques for checkpoint 11.1
   
      11.2 Current author bindings. (P2)
      
    1. Provide a centralized view of the current author-specified input
       configuration bindings.
    2. The user agent may satisfy this checkpoint by providing different
       views for different input modalities (keyboard, pointing device,
       voice, etc.).
       
   For all content. Techniques for checkpoint 11.2
   
   Note: For example, for HTML documents, provide a view of keyboard
   bindings specified by the author through the "accesskey" attribute.
   The intent of this checkpoint is to centralize information about
   author-specified bindings so that the user does not have to read the
   entire content first to find out what bindings are available.
   
      11.3 Override bindings. (P2)
      
    1. Allow the user to override any binding that is part of the user
       agent default input configuration.
    2. The user agent is not required to allow the user to override
       conventional bindings for the operating environment (e.g., for
       access to help).
    3. The override requirement only applies to bindings for the same
       input modality (e.g., the user must be able to override a keyboard
       binding with another keyboard binding).
       
   For user agent features. Techniques for checkpoint 11.3
   
   Note: See also checkpoint 11.5, checkpoint 11.7, and checkpoint 12.3.
   
      11.4 Single key access. (P2)
      
    1. Allow the user to override any binding in the user agent default
       keyboard configuration with a binding to either a key plus
       modifier keys or to a single-key. In this checkpoint, "key" refers
       to a physical key of the keyboard (rather than, say, a character
       of the document character set).
    2. For each functionality in the set required by checkpoint 11.5,
       allow the user to configure a single-key binding (i.e., one key
       press performs the task, with zero modifier keys).
    3. If the number of physical keys on the keyboard is less than the
       number of functionalities required by checkpoint 11.5, allow
       single-key bindings for as many of those functionalities as
       possible.
    4. The single-key binding requirements may be satisfied with a
       "single-key mode" (i.e., a mode where the current bindings are
       replaced by a set of single-key bindings).
    5. The user agent is not required to allow the user to override
       conventional bindings for the operating environment (e.g., for
       access to help).
    6. This checkpoint does not require single physical key bindings for
       character input, only for the activation of user agent
       functionalities.
       
   For user agent features. Techniques for checkpoint 11.4
   
   Note: Because single-key access is so important to some users with
   physical disabilities, user agents should ensure that (1) most keys of
   the physical keyboard may be configured for single-key bindings, and
   (2) most functionalities of the user agent may be configured for
   single-key bindings. For information about access to user agent
   functionality through a keyboard API, see checkpoint 6.6.
   
      11.5 Default binding requirements. (P2)
      
    1. Ensure that the user agent default input configuration includes
       bindings for the following functionalities required by other
       checkpoints in this document:
          + move focus to next enabled element, and move focus to
            previous enabled element;
          + activate focused link;
          + search for text;
          + search again for same text;
          + increase size of rendered text, and decrease size of rendered
            text;
          + increase global volume, and decrease global volume;
          + stop, pause, resume, and navigate efficiently selected audio
            and animations (including video and animated images).
    2. If the user agent supports the following functionalities, the
       default input configuration must also include bindings for them:
          + next history state (forward), and previous history state
            (back);
          + enter URI for new resource;
          + add to favorites (i.e., bookmarked resources);
          + view favorites;
          + stop loading resource;
          + reload resource;
          + refresh rendering;
          + forward one viewport, and back one viewport;
          + next line, and previous line.
       
   For user agent features. Techniques for checkpoint 11.5
   
   Note: This checkpoint does not make any requirements about the ease of
   use of default input configurations, though clearly the default
   configuration should include single-key bindings and allow easy
   operation. Ease of use is ensured by the configuration requirements of
   checkpoint 11.3.
   
      11.6 User profiles. (P2)
      
    1. For the configuration requirements of this document, allow the
       user to save user preferences in at least one user profile.
    2. Allow the user to choose from among available default profiles,
       profiles created by the same user, and no profile (i.e., the user
       agent default settings).
       
   For user agent features. Techniques for checkpoint 11.6
   
      11.7 Configure tool bars. (P3)
      
    1. For graphical user interfaces, allow the user to configure the
       position of controls on tool bars of the user agent user
       interface, to add or remove controls for the user interface from a
       predefined set, and to restore the default user interface.
       
   For user agent features. Techniques for checkpoint 11.7
   
   Note: This checkpoint is a special case of checkpoint 11.3.
   
   [next guideline 12] [review guideline 11] [previous guideline 10]
   [contents]
   
Guideline 12. Provide accessible user agent documentation and help.

    Ensure that the user can learn about software features that benefit
    accessibility from the documentation. Ensure that the documentation is
    accessible.
    
   Documentation of the user interface is important, as is documentation
   of the user agent's underlying functionalities. While intuitive user
   interface design is valuable to many users, some users may still not
   be able to understand or be able to operate the native user interface
   without thorough documentation (e.g., a user with blindness may not
   find a graphical user interface intuitive without supporting
   documentation).
   
   There are three types of requirements in this guideline:
    1. accessibility of the documentation (checkpoint 12.1);
    2. minimal requirements of what must be documented (checkpoint 12.2,
       checkpoint 12.3, and checkpoint 12.4). Documentation should
       include much more to explain how to install, get help for, use, or
       configure the user agent;
    3. organization of the documentation (checkpoint 12.5).
       
   Refer to checkpoint 7.3 for information about following system
   conventions for documentation.
   
    Checkpoints
    
      12.1 Accessible documentation. (P1)
      
    1. Ensure that at least one version of the user agent documentation
       conforms to at least Level Double-A of the Web Content
       Accessibility Guidelines 1.0 [WCAG10].
       
   For user agent features. Techniques for checkpoint 12.1
   
      12.2 Document accessibility features. (P1)
      
    1. Document all user agent features that benefit accessibility.
    2. For the purposes of this checkpoint, a user agent feature that
       benefits accessibility is one implemented to satisfy the
       requirements of this document (including the requirements of
       checkpoints 8.1 and 7.3).
    3. The user agent may satisfy this checkpoint either by
          + providing a centralized view of the accessibility features,
            or
          + integrating accessibility features into the rest of the
            documentation.
       
   For user agent features. Techniques for checkpoint 12.2
   
   Note: The help system should include discussion of user agent features
   that benefit accessibility. The user agent should satisfy this
   checkpoint by providing both centralized and integrated views of
   accessibility features in the documentation.
   
      12.3 Document default bindings. (P1)
      
    1. Document the default user agent input configuration (e.g., the
       default keyboard bindings).
       
   For user agent features. Techniques for checkpoint 12.3
   
   Note: If the default input configuration is inconsistent with
   conventions of the operating environment, the documentation should
   alert the user.
   
      12.4 Document changes. (P2)
      
    1. Document changes from the previous version of the user agent to
       accessibility features, including accessibility features of the
       user interface.
    2. Accessibility features are those defined in checkpoint 12.2.
       
   For user agent features. Techniques for checkpoint 12.4
   
      12.5 Dedicated section on accessibility. (P2)
      
    1. Provide a centralized view of all features of the user agent that
       benefit accessibility in a dedicated section of the documentation.
    2. The features that benefit accessibility are those defined in
       checkpoint 12.2.
       
   For user agent features. Techniques for checkpoint 12.5
   
   Note: The user agent satisfies this checkpoint automatically by
   providing a centralized view of accessibility features to satisfy
   checkpoint 12.2. However, developers are encouraged to integrate
   descriptions of accessibility features into the documentation
   alongside other features, in addition to providing a centralized view.
   
   [review guideline 12] [previous guideline 11] [contents]
   
3. Conformance

   This normative section defines what it means to conform to this
   document and explains how to make a valid conformance claim. The
   following are important conformance concepts.
     * Conformance and conformance claims differ. This document
       distinguishes conformance requirements and conformance claim
       requirements. The sections on unconditional conformance and
       conditional conformance explain the conformance requirements. The
       section on well-formed claims explains the claim requirements
       (e.g., identification of the components that make up the user
       agent, the operating environment in which they run, etc.) Here is
       a sample claim (expressed in HTML):
       <p>On 12 September 2001, Project X (version 2.3) running on
       MyOperatingSystem (version 4.2) conforms to <abbr title="the World
       Wide Web Consortium">W3C</abbr>'s "User Agent Accessibility
       Guidelines 1.0", http://www.w3.org/TR/2001/CR-UAAG10-20010912,
       level Double-A. Unsupported content types: Video, Speech.
       Unsupported input modalities: Voice. (see section 3.1 of the UAAG
       1.0). The <a href="http://example.com/checkpoints">list of
       checkpoints that do not apply</a> is available online.</p>
     * Modular conformance. A conforming user agent is not required to be
       a single piece of software. In general, a conforming user agent
       will consist of several coordinated components, such as a browser,
       a multimedia player, documentation on the Web, etc. The current
       document places no restrictions on the type or number of
       components that make up the "subject of a conformance claim",
       i.e., the user agent (i.e., set of components) about which someone
       has made a conformance claim.
     * Conditional conformance. A user agent is not required to satisfy
       every checkpoint in order to conform. This document allows
       "conditional conformance", which means conformance to less than
       (or more than) a default set of requirements. Claimants may not
       pick and choose which requirements they wish to satisfy in order
       to conform conditionally; conditional conformance is governed by
       several mechanisms described below:
         1. conformance levels,
         2. content type labels,
         3. input modality labels,
         4. selection label.
       When a user agent conforms conditionally, a conformance claim
       about the user agent must indicate how the set of satisfied
       requirements differs from the default set; see the section on
       well-formed claims.
     * Applicability. Some checkpoints may not apply to a particular user
       agent because of the nature of the user agent's user interface or
       the nature of the format(s) implemented by the user agent. If a
       checkpoint (or portion of a checkpoint) doesn't apply, the user
       agent is not required to satisfy it for conformance. A claimant
       must state in a well-formed conformance claim which checkpoints,
       if any, do not apply. See the section on applicability for
       information about how to determine whether a checkpoint applies.
       
   In this document (notably in the checkpoints and in this section on
   conformance), the terms "must", "should", and "may" (and related
   terms) are used in accordance with RFC 2119 [RFC2119].
   
   Note: Conformance to the requirements of this document is expected to
   be a strong indicator of accessibility, but it is neither a necessary
   nor sufficient condition for ensuring the accessibility of software.
   Some software may not conform to this document but still be accessible
   to some users with disabilities. Conversely, some software may conform
   to this document but still be inaccessible to some users with
   disabilities. Some requirements of this document may not benefit some
   users for some content, but the requirements are expected to benefit
   many users with disabilities, for general purpose content. For more
   information, please see the sections on known limitations of this
   document and restricted functionality and conformance.
   
  3.1 Unconditional conformance
  
   A user agent conforms unconditionally to this document if:
    1. it satisfies all of the requirements of all the checkpoints. Note
       that each checkpoint statement includes one or more requirements.
       The requirements made by a checkpoint include those associated
       with any content type labels for that checkpoint. Certain
       checkpoints also include labels that indicate (when there might be
       ambiguity) whether the requirements are for all content, for all
       rendered content, for user agent features, or for both user agent
       features and content;
    2. for each checkpoint in guideline 6, it satisfies the requirements
       by implementing APIs. For every other checkpoint, it satisfies the
       requirements by implementing at least one mechanism other than an
       API. Note: The checkpoints outside of guideline 6 may be satisfied
       by assistive technologies as well, but are required by the current
       document to be satisfied by a conforming user agent. For example,
       checkpoint 9.3 involves navigation that must be possible through
       the user interface, not just via an API. Note that an assistive
       technology may be part of the subject of a claim.
       
   These requirements together form the "default" set of conformance
   requirements.
   
  3.2 Conditional conformance
  
   To allow user agents with different capabilities to conform, and to
   facilitate comparisons of claims about different user agents, this
   document defines allows conditional conformance. A user agent conforms
   conditionally if it satisfies any set of requirements that results
   from starting with the default set of requirements and removing or
   adding requirements according to these steps:
    1. Choose a conformance level; conformance levels A or Double-A
       remove requirements from the default set.
    2. Remove the requirements associated with any unsupported content
       type labels. In order to conform conditionally, a user agent must
       satisfy the requirements of at least one content type label.
    3. Add requirements associated with any supported input modality
       label. Note: In the default set of requirements, the only input
       device requirements relate to keyboard input.
    4. If the user agent does not implement a selection mechanism, remove
       the requirements of any checkpoints or parts of checkpoints
       associated with the selection label.
    5. Remove the requirements of any checkpoints or parts of checkpoints
       that do not apply.
       
   Since these steps may produce very different sets of checkpoints for
   different user agents, a well-formed conformance claim must indicate
   how the set of requirements chosen for the claim differs from the
   default set. The checklist [UAAG10-CHECKLIST] may prove useful when
   documenting the details of a conditional conformance claim.
   
    Example of a conditional conformance requirement set
    
   The following example illustrates how to apply the above steps to
   determine which requirements must be satisfied for conformance, and
   what would be required as part of a well-formed conformance claim.
   This informative example does not illustrate a complete user agent
   evaluation.
   
   Consider a user agent with these capabilities:
     * it supports keyboard and pointing device input;
     * it renders text (in color) and implements:
          + one audio format,
          + two image formats,
          + two other animation formats (besides video, which is
            considered an animation format in this document);
     * it feeds video to a plug-in for rendering;
     * it doesn't support synthesized speech output;
     * it implements a selection mechanism.
       
      Step 1: Choose a conformance level.
      
   The claimant wishes to conform at level Double-A. This establishes a
   set of requirements consisting of all of the requirements of all the
   priority 1 and 2 checkpoints.
   
      Step 2: Remove the requirements associated with any unsupported content
      type labels.
      
   The claimant wishes to claim conformance for the user agent's support
   of text, images, audio, and video. The claimant does not wish to claim
   conformance for other animation formats.
   
   The following content type labels are therefore relevant: VisualText,
   ColorText, Image, Animation, Video, and Audio. This means that:
     * the claimant must remove the set of requirements associated with
       the Speech content type label.
     * the claimant must satisfy the requirements associated with the
       other content type labels.
       
      Step 3: Remove the requirements of any checkpoints or parts of
      checkpoints that do not apply.
      
   Consider checkpoint 4.4, for example, which is associated with both
   the Audio and Animation content type labels:
   
      4.4 Slow multimedia. (P1)
      
    1. Allow the user to slow the presentation rate of rendered audio and
       animations (including video and animated images).
    2. For a visual track, provide at least one setting between 40% and
       60% of the original speed.
    3. For a prerecorded audio track including audio-only presentations,
       provide at least one setting between 75% and 80% of the original
       speed.
    4. When the user agent allows the user to slow the visual track of a
       synchronized multimedia presentation to between 100% and 80% of
       its original speed, synchronize the visual and audio tracks. Below
       80%, the user agent is not required to render the audio track.
    5. The user agent is not required to satisfy this checkpoint for
       audio and animations whose recognized role is to create a purely
       stylistic effect.
       
   Suppose that:
    1. The claimant wishes to claim support for the two image formats,
       the one audio format, and the one video format;
    2. The claimant does not wish to claim support for the other two
       animation formats (e.g., because the user agent doesn't satisfy
       the requirements of checkpoint 4.4 for those animation formats);
    3. The user agent does not implement any synchronized multimedia
       formats.
       
   The resulting applicable requirements from this checkpoint would be:
     * For the audio format: Allow the user to slow the presentation rate
       of audio. For a prerecorded audio track including audio-only
       presentations, provide at least one setting between 75% and 80% of
       the original speed.
     * For the video format: Allow the user to slow the presentation rate
       of video. For a visual track, provide at least one setting between
       40% and 60% of the original speed.
     * For the image formats: None, since the Image content type label
       does not include checkpoint 4.4.
     * Limitation of scope for any format: The user agent is not required
       to satisfy the requirements of this checkpoint for audio and
       animations whose recognized role is to create a purely stylistic
       effect.
       
   The following requirements would not apply:
     * When the user agent allows the user to slow the visual track of a
       synchronized multimedia presentation to between 100% and 80% of
       its original speed, synchronize the visual and audio tracks. Below
       80%, the user agent is not required to render the audio track.
       Note: The relevant applicability provision is provision three:
       control of a content property that the subject cannot recognize.
       In this case, no format implemented by the user agent supports
       synchronized multimedia.
       
      Step 4: Add requirements related to the selection.
      
   In this example, since the user agent implements a selection
   mechanism, it must satisfy the requirements associated with the
   selection label.
   
      Step 5: Add requirements associated with any supported input modality
      label.
      
   In this example, the claimant does not wish to claim conformance for
   complete operation for pointing device or voice input, so no
   requirements are added.
   
      Construct a well-formed conformance claim.
      
   The following information is an excerpt of that required for a
   well-formed claim:
     * Conformance level satisfied: Double-A
     * Information about the subject. Both the "main" user agent and the
       plug-in used to support video must be identified in the claim
       (since the plug-in is the component used to satisfy the
       requirements for video).
       
   The user agent does not conform unconditionally, therefore, the claim
   must also include the following information (excerpted from a complete
   claim):
     * A general statement about lack of support for the Speech content
       type label: "This user agent does not support the requirements of
       the Speech content type label. "
     * A specific statement about content type support for checkpoint
       4.4: "This user agent satisfies the requirements of the Animation
       content type label for the audio format A and the video format V.
       It does not satisfy the Animation requirements for animation
       formats Y and Z."
     * A specific statement about applicability for checkpoint 4.4: "The
       synchronized multimedia requirements of checkpoint checkpoint 4.4
       do not apply because the user agent does not implement any formats
       that support synchronized multimedia."
       
  3.3 Conformance details
  
   The following normative subsections provide detail that is relevant to
   both unconditional and conditional conformance.
   
    Requirements for content, for rendered content, for user agent features, or
    both user agent features and content
    
   The requirements of certain checkpoints might apply equally well to
   content or to user agent user interface features. When it is necessary
   to remove ambiguity about the scope of a checkpoint, the checkpoint
   includes a label to indicate whether the requirements must be
   satisfied:
    1. for content only, i.e., the document object only;
    2. for rendered content only;
    3. for user agent features only, i.e., everything that is not content
       (such as components of the user agent user interface, user
       preferences, the user agent documentation, and the user interface
       focus);
    4. for both content and user agent features.
       
   Many of the content-only and rendered content-only requirements also
   make sense for the user agent user interface (e.g., allow the user to
   render blinking text as motionless text). User agent developers are
   encouraged to consider the content-only requirements when designing
   the user agent's user interface.
   
   The user agent may satisfy a content-only or rendered content-only
   requirement with a mechanism that also involves user agent features.
   For instance, to satisfy checkpoint 4.9, the user agent may provide a
   single control for all volume (including content and user interface
   features). Similarly, to satisfy checkpoint 3.3, the user agent may
   offer a single configuration that turns off blinking in both content
   and the user interface.
   
    Conformance and implementing specifications
    
   A user agent may conform by satisfying the checkpoint requirements of
   this document for some, but not all, implemented specifications and
   APIs. For example, a developer may implement ten image formats but
   only wish to claim "Image" conformance for three of them.
   
   In particular, the following requirements may be satisfied for some
   but not all implemented specifications:
     * requirements associated with a content type label;
     * the API requirements of checkpoint checkpoint 6.3, checkpoint 6.4,
       and checkpoint 6.5.
     * the rendering requirements of checkpoints 2.1 and 2.2;
     * the format requirements of checkpoints 8.1 and 8.2.
       
    Configuration requirements
    
   The user agent may satisfy the configuration requirements of this
   document through configuration files (e.g., profiles, initialization
   files, themes, etc.). For instance, style sheets might be used as a
   mechanism to satisfy the highlight and configuration requirements of
   checkpoints 10.2 and 10.4. Any functionality that is configurable
   through a configuration file should also be configurable through the
   user agent user interface. Furthermore, if configuration files may be
   edited by hand, the user agent documentation should explain the
   configuration file format, or refer to an explanation (such as a
   format specification).
   
   For some of the checkpoints in this document (checkpoint 3.3,
   checkpoint 5.1, checkpoint 5.3, checkpoint 5.5, checkpoint 5.6),
   configuration is preferred, but not required to satisfy the checkpoint
   in some circumstances. For other checkpoints, the configuration
   requirement is considered as important as the functionality being
   configured.
   
   Since this document allows conformance by multiple software components
   (e.g., a browser, a media player, and several plug-ins), there are
   likely to be times when, to satisfy the configuration requirements of
   the document, each component has to provide for configuration
   independently. To make configuration easier for the user, components
   should share and inherit configurations (including from the operating
   environment).
   
    Use of operating environment features as part of conformance
    
   To satisfy the requirements of this document, developers are
   encouraged to adopt operating environment conventions and features
   that benefit accessibility. When an operating environment feature
   (e.g., the operating system's audio control feature, including its
   user interface) is adopted to satisfy the requirements of this
   document, it is part of the subject of the claim.
   
   Developers may provide access through the user agent's user interface
   to operating environment features adopted to satisfy the requirements
   of this document. For example, if the user agent adopts the operating
   system's audio control feature to satisfy checkpoint 4.9, the user
   agent may (but is not required to) include those controls in its own
   user interface.
   
   Some of the checkpoints in this document involve operating environment
   conventions. When a user agent runs in more than one operating
   environment (e.g., a user agent implemented in Java on top of another
   operating system), developers may satisfy the requirements of this
   document by following the conventions of a single operating
   environment. Developers should follow the conventions that benefit
   accessibility most, while meeting the developers' design goals. For
   instance, some developers may prefer cross-platform consistency over
   consistency with other user agents running in a given operating
   environment, and this might affect which conventions would be
   preferred.
   
    Restricted functionality and conformance
    
   User agents do not conform to this document on a per-resource basis;
   claims are not as specific as "the user agent conforms for this
   particular Web page." A user agent conforms if it satisfies the
   requirements of this document for most general-purpose content, in
   ordinary operating conditions.
   
   In some cases, an author may wish to limit the user agent's
   functionality for specific reasons, such as to protect intellectual
   property rights, for security reasons, or to provide a read-only view
   (allowing no user interaction). Content that limits the functionality
   of the user agent in some cases does not automatically invalidate a
   conformance claim. A valid conformance claim remains valid as long as
   the user agent is capable of satisfying the requirements of the
   document (i.e., the functionalities have been implemented), and does
   so for most general-purpose content.
   
   Note: The User Agent Accessibility Guidelines Working Group recognizes
   that further work is necessary in the area of digital rights
   management as it relates to accessibility. Digital rights management
   refers to methods of describing and perhaps enforcing intellectual
   property associated with Web resources.
   
  3.4 Conformance levels
  
   Each conformance level defines a set of requirements, based on
   priority.
     * Conformance Level "A": the requirements of all Priority 1
       checkpoints.
     * Conformance Level "Double-A": the requirements of all Priority 1
       and 2 checkpoints.
     * Conformance Level "Triple-A": the requirements of all Priority 1,
       2, and 3 checkpoints.
       
   Note: Conformance levels are spelled out in text (e.g., "Double-A"
   rather than "AA") so they may be understood when rendered as
   synchronized speech.
   
  3.5 Content type labels
  
   Each content type label defines a set of requirements related to
   support for images, video, animations generally, visually displayed
   text (in color), and synthesized speech.
   
   VisualText
          This content type label refers to all of the requirements
          related to the visual rendering of text for the following
          checkpoints: 3.3, 4.1, and 4.2. To conform, the user agent must
          support visually rendered text.
          
   ColorText
          This content type label refers to all of the requirements
          related to text foreground and background color for the
          following checkpoint: 10.4. To conform, the user agent must
          support more than one text foreground color and more than one
          text background color.
          
   Image
          This content type label refers to all of the requirements
          related to images (excluding animated images) for the following
          checkpoints: 3.1, and 3.7. To conform, the user agent must
          implement at least one image format. The image requirements
          apply to content that is recognized as distinct and that,
          according to the encoding format, may be rendered as a coherent
          unit.
          
   Animation
          This content type label refers to all of the requirements
          related to animations (including video and animated images) for
          the following checkpoints: 3.2, 4.4, 4.5, 4.7, and 4.8. To
          conform, the user agent must implement at least one animation
          format. The animation requirements apply to animation content
          that is recognized as distinct and that, according to the
          encoding format, may be rendered as a coherent unit.
          
   Video
          This content type label refers to all of the requirements
          related to video for the following checkpoints: 2.5, 2.6, and
          3.2. To conform, the user agent must implement at least one
          video format. The video requirements apply to video content
          that is recognized as distinct and that, according to the
          encoding format, may be rendered as a coherent unit.
          
   Audio
          This content type label refers to all of the requirements
          related to audio for the following checkpoints: 2.5, 2.6, 3.2,
          4.4, 4.5, 4.7, 4.8, 4.9, 4.10, and 4.11 To conform, the user
          agent must implement at least one audio format. The audio
          requirements apply to audio content that is recognized as
          distinct and that, according to the encoding format, may be
          rendered as a coherent unit.
          
   Speech
          This content type label refers to all of the requirements
          related to synthesized speech for the following checkpoints:
          4.12, 4.13, 4.14, 4.15, and 4.16. To conform, the user agent
          must support synthesized speech.
          
   Note: Some of the labels above require implementation of at least one
   format (e.g., for images). This document does not require
   implementation of specific formats, (e.g., PNG [PNG] versus SVG [SVG]
   for images). However, please see the requirements of checkpoint 8.2.
   
  3.6 Input modality labels
  
   Each input modality label defines a set of requirements related to
   support for pointing device and voice input. Input device requirements
   in this document are either stated generically (e.g., "input
   configuration" requirements) or as keyboard-specific requirements
   (e.g., "keyboard API").
   
   Pointer
          This input modality label refers to all of the input device
          requirements of this document, applied to pointing device
          input. For keyboard-specific requirements, substitute "pointing
          device input" for "keyboard." The set of pointing device input
          requirements does not include the requirements of checkpoint
          11.4.
          
   Voice
          This input modality label refers to all of the input device
          requirements of this document, applied to voice input. For
          keyboard-specific requirements, substitute "voice input" for
          "keyboard." The set of voice input requirements does not
          include the requirements of checkpoint 11.4.
          
   Note: Developers are encouraged to design user agents that are at
   least partially operable through all three input modalities.
   
  3.7 Selection label
  
   This document does not require the user agent to implement a selection
   mechanism in order to conform. However, if the user agent does
   implement a selection mechanism, in order to conform it must satisfy
   the relevant portions of the following checkpoints: 6.5, 7.1, 9.4,
   10.2, 10.3, and 5.4. The Selection label refers to the selection
   requirements of these checkpoints.
   
   If a user agent does not implement a selection mechanism, then a
   well-formed claim must say so.
   
   Note: This document does require implementation of both content focus
   and user interface focus; see checkpoint 9.1 and checkpoint 9.2.
   
  3.8 Checkpoint applicability
  
   A checkpoint (or part of a checkpoint) applies unless any one of the
   following conditions is met:
    1. The checkpoint makes requirements for graphical user interfaces or
       graphical viewports and the subject of the claim only has audio or
       tactile user interfaces or viewports.
    2. The checkpoint refers to a role of content (e.g., transcript,
       captions, associated conditional content, fee link,
       synchronization cue, client-side redirect, purpose of a table,
       etc.) that the subject of the claim cannot recognize because of
       how the content has been encoded in a particular format. For
       instance, HTML user agents can recognize "alt", OBJECT content, or
       NOFRAMES content as specified mechanisms for conditional content.
       HTML user agents are not expected to recognize that a nearby
       paragraph is a text equivalent for the image (when not marked up
       as such).
    3. The checkpoint requires control of a content property that the
       subject cannot recognize because of how the content has been
       encoded in a particular format. Some examples of this include:
          + captioning information that is "burned" into a video
            presentation and cannot be recognized as captions in the
            presentation format;
          + streamed content that cannot be fast forwarded or rewound;
          + information encoded in an unrecognized XML namespace;
          + information or relationships encoded in scripts in a manner
            that cannot be recognized. For instance, the requirements of
            checkpoint 3.3 would not apply for animation effects
            unrecognized in a script. Some input device behavior may be
            controlled by scripts in a manner that the user agent cannot
            recognize. For example, when the author uses event bubbling
            to dispatch events, the user agent is not likely to recognize
            the full set of elements that may receive those events; the
            user agent is expected to recognize which element has the
            explicitly associated event handler.
       
  3.9 Well-formed conformance claims
  
   A claim is well-formed if meets the following conditions.
   
   Condition 1: The claim must include the following information:
    1. The date of the claim.
    2. The guidelines title/version: "User Agent Accessibility Guidelines
       1.0".
    3. The URI of the guidelines:
       http://www.w3.org/TR/2001/CR-UAAG10-20010912.
    4. The conformance level satisfied: "A", "Double-A", or "Triple-A".
    5. Information about the subject. The subject of the claim may
       consist of one or more software components (e.g., a browser plus a
       multimedia player plus a plug-in). For each component, the claim
       must include the following:
          + The user agent name and version information. Version
            information must be sufficient to identify the user agent
            (e.g., vendor name, version number, minor release number,
            required patches or updates, natural language of the user
            interface or documentation). The version information may
            refer to a range of user agents (e.g., "this claim refers to
            all user agents version 6.x").
          + The name and version number of the operating environment(s)
            in which the user agent is running.
          + If a conformance icon is part of a claim on the Web, it must
            link to the W3C explanation of the icon.
       
   Condition 2: The claim must include the following information if the
   user agent conforms conditionally:
    1. Content type labels. Content type labels are used in assertions
       that the subject either (1) does not satisfy the requirements
       associated with the label (e.g., for a specific checkpoint, for
       any checkpoint, etc.), or (2) does satisfy the requirements
       associated with the label (e.g., for a particular format when
       satisfying the requirements of a checkpoint). In order to conform
       conditionally, a user agent must satisfy the requirements of at
       least one content type label.
    2. Input modality labels. Each input modality label ("Pointer" or
       "Voice") is an assertion that the user agent satisfies the
       requirements associated with the label.
    3. Selection label. If the user agent does not implement a selection
       mechanism, the claim must say so.
    4. A list of requirements (checkpoints or portions of checkpoints)
       that the claim asserts do not apply.
       
   Condition 3: At least one version of the claim must conform to the
   "Web Content Accessibility Guidelines 1.0" [WCAG10], level A. This
   claim may appear on the Web, on a CD-ROM, etc.
   
   A well-formed claim should also include the following information:
     * Information about which specifications have been implemented to
       satisfy the requirements of the document (e.g., those of guideline
       6 and guideline 8).
     * Rationale for any requirements that do not apply.
       
   This specification imposes no restrictions on the format used to make
   a well-formed claim. For instance, the claim may be marked up using
   HTML (see sample claim), or expressed in the Resource Description
   Framework (RDF) [RDF10].
   
  3.10 Validity of a claim
  
   A conformance claim is valid if the following conditions are met:
    1. The claim is well-formed.
    2. It is verified that the user agent satisfies the default set of
       requirements, in addition to (or except) those requirements added
       (or exempted) by the allowable mechanisms: conformance levels,
       content type labels, input modality labels, and applicability.
       
   It is not currently possible to validate a claim entirely
   automatically.
   
   Notes:
     * The subject of the claim may consist of more than one software
       component, and taken together they must satisfy all requirements
       that are not excluded through the claim. These components may run
       on the user's computer or on a server. This includes assistive
       technologies and operating environment features that are part of a
       claim. Some components may not have to satisfy some requirements
       as long as the subject as a whole satisfies them. For instance, a
       particular component of the subject may not have to conform to the
       DOM APIs required by guideline 6 as long as the subject of the
       claim as a whole makes all content available through those APIs.
     * The document has been designed so that non-experts can determine
       the validity of a claim. In some cases, a requirement might be
       clear, but without documentation or feedback from developers
       (e.g., about implemented APIs), it may be difficult to verify that
       the subject of the claim has satisfied the requirement. Some
       checkpoints (e.g., those requiring developers to follow
       conventions or implement specifications defined outside this
       document) are inherently more open to interpretation than others.
     * Ideally, the default user agent installation procedure should
       provide and install all components that are part of a conformance
       claim. This is because, the more software components the user must
       install in order to construct a conforming user agent, the higher
       the risk of failure. Failure may be due to inaccessible mechanisms
       for downloading and installing plug-ins, or lack of installation
       access privileges for a computer in a public space, etc.
       
    Responsibility for claims
    
   This specification imposes no restrictions about:
     * who may make a claim (e.g., vendors about their own user agents,
       third parties about those user agents, journalists about user
       agents, etc.), or
     * where claims may be published (e.g., on the Web or in paper
       documentation).
       
   Claimants (or relevant assuring parties) are solely responsible for
   the validity of their claims, keeping claims up to date, and proper
   use of the conformance icons. As of the publication of this document,
   W3C does not act as an assuring party, but it may do so in the future,
   or it may establish recommendations for assuring parties.
   
   Claimants are expected to modify or retract a claim if it may be
   demonstrated that the claim is not valid. Claimants are encouraged to
   claim conformance to the most recent User Agent Accessibility
   Guidelines Recommendation available.
   
    Conformance icons
    
   As part of a conformance claim, people may use a conformance icon (or,
   "conformance logo") on a Web site, on user agent packaging, in
   documentation, etc. A conformance icon does not represent that a claim
   is valid, only that a claim has been made. The appearance of a
   conformance icon does not imply that W3C has reviewed the claim.
   
   It is inappropriate and meaningless to use a conformance icon on its
   own, i.e., to use the icon without an associated well-formed claim.
   
   Draft Note: In the event this document becomes a W3C Recommendation
   this document will link to the W3C Web site for additional information
   about the icons and how to use them.
   
4. Glossary

   This glossary is normative. Some terms (or parts of explanations of
   terms) may not have an impact on conformance.
   
   Note: In this document, glossary terms generally link to the
   corresponding entries in this section. These terms are also
   highlighted through style sheets and identified as glossary terms
   through markup.
   
   a · b · c · d · e · f · g · h · i · j · k · l · m · n · o · p · q · r
   · s · t · u · v · w · x · y · z
   
   Activate
          In this document, the verb "to activate" means (depending on
          context) either:
          
          + To execute or carry out one or more behaviors associated with
            an enabled element.
          + To execute or carry out one or more behaviors associated with
            a component of the user agent user interface.
            
          The effect of activation depends on the type of enabled element
          or user interface control. For instance, when a link is
          activated, the user agent generally retrieves the linked Web
          resource. When a form element is activated, it may change state
          (e.g., check boxes) or may take user input (e.g., a text entry
          field).
          
   Alert
          In this document, "to alert" means to make the user aware of
          some event, without requiring acknowledgement. For example, the
          user agent may alert the user that new content is available on
          the server by displaying a text message in the user agent's
          status bar. See checkpoint 1.3 for requirements about alerts.
          
   Animation
          In this document, an "animation" refers to content that, when
          rendered, creates a visual movement effect automatically (i.e.,
          without manual user interaction). This definition of animation
          includes video and animated images. Animation techniques
          include:
          
          + graphically displaying a sequence of snapshots within the
            same region (e.g., as is done for video and animated images).
            The series of snapshots may be provided by a single resource
            (e.g., an animated GIF image) or from distinct resources
            (e.g., a series of images downloaded continuously by the user
            agent).
          + scrolling text (e.g., achieved through markup or style
            sheets).
          + displacing graphical objects around the viewport (e.g., a
            picture of a ball that is moved around the viewport giving
            the impression that it is bouncing off of the viewport
            edges). For instance, the SMIL 2.0 [SMIL20] animation modules
            explain how to create such animation effects in a declarative
            manner (i.e., not by composition of successive snapshots).
            
   Applet
          An applet is a program (generally written in the Java
          programming language) that is part of content, and that the
          user agent executes.
          
   Application Programming Interface (API), conventional
          input/output/device API
          An application programming interface (API) defines how
          communication may take place between applications.
          
          Implementing APIs that are independent of a particular
          operating environment (as are the W3C DOM Level 2
          specifications) may reduce implementation costs for
          multi-platform user agents and promote the development of
          multi-platform assistive technologies. Implementing
          conventional APIs for a particular operating environment may
          reduce implementation costs for assistive technology developers
          who wish to interoperate with more than one piece of software
          running on that operating environment.
          
          A "device API" defines how communication may take place with an
          input or output device such as a keyboard, mouse, video card,
          etc.
          
          In this document, an "input/output API" defines how
          applications or devices communicate with a user agent. As used
          in this document, input and output APIs include, but are not
          limited to, device APIs. Input and output APIs also include
          more abstract communication interfaces than those specified by
          device APIs. A "conventional input/output API" is one that is
          expected to be implemented by software running on a particular
          operating environment. For example, on desktop computers today,
          the conventional input APIs are for the mouse and keyboard. For
          touch screen devices or mobile devices, conventional input APIs
          may include stylus, buttons, voice, etc. The graphical display
          and sound card are considered conventional ouput devices for a
          graphical desktop computer environment, and each has an
          associated API.
          
   Assistive technology
          In the context of this document, an assistive technology is a
          user agent that:
          
         1. relies on services (such as retrieving Web resources, parsing
            markup, etc.) provided by one or more other "host" user
            agents. Assistive technologies communicate data and messages
            with host user agents by using and monitoring APIs.
         2. provides services beyond those offered by the host user
            agents to meet the requirements of users with disabilities.
            Additional services include alternative renderings (e.g., as
            synthesized speech or magnified content), alternative input
            methods (e.g., voice), additional navigation or orientation
            mechanisms, content transformations (e.g., to make tables
            more accessible), etc.
            
          For example, screen reader software is an assistive technology
          because it relies on browsers or other software to enable Web
          access, particularly for people with visual and learning
          disabilities.
          
          Examples of assistive technologies that are important in the
          context of this document include the following:
          
          + screen magnifiers, which are used by people with visual
            disabilities to enlarge and change colors on the screen to
            improve the visual readability of rendered text and images.
          + screen readers, which are used by people who are blind or
            have reading disabilities to read textual information through
            synthesized speech or braille displays.
          + voice recognition software, which may be used by people who
            have some physical disabilities.
          + alternative keyboards, which are used by people with certain
            physical disabilities to simulate the keyboard.
          + alternative pointing devices, which are used by people with
            certain physical disabilities to simulate mouse pointing and
            button activations.
            
          Beyond this document, assistive technologies consist of
          software or hardware that has been specifically designed to
          assist people with disabilities in carrying out daily
          activities, e.g., wheelchairs, reading machines, devices for
          grasping, text telephones, vibrating pagers, etc. For example,
          the following very general definition of "assistive technology
          device" comes from the (U.S.) Assistive Technology Act of 1998
          [AT1998]:
          
     Any item, piece of equipment, or product system, whether acquired
     commercially, modified, or customized, that is used to increase,
     maintain, or improve functional capabilities of individuals with
     disabilities.
     
   Attribute
          This document uses the term "attribute" in the XML sense: an
          element may have a set of attribute specifications (refer to
          the XML 1.0 specification [XML] section 3).
          
   Audio
          In this document, the term "audio" refers to content that
          encodes pre-recorded sound.
          
   Audio-only presentation
          An audio-only presentation is content consisting exclusively of
          one or more audio tracks presented concurrently or in series.
          Examples of an audio-only presentation include a musical
          performance, a radio-style news broadcast, and a narration.
          
   Audio track
          An audio object is content rendered as sound through an audio
          viewport. An audio track is an audio object that is intended as
          a whole or partial presentation. An audio track may, but is not
          required to, correspond to a single audio channel (left or
          right audio channel).
          
   Auditory description
          An auditory description (sometimes, "audio description") is
          either a prerecorded human voice or a synthesized voice
          (recorded or generated dynamically) describing the key visual
          elements of a movie or other animation. The auditory
          description is synchronized with (and possibly included as part
          of) the audio track of the presentation, usually during natural
          pauses in the audio track. Auditory descriptions include
          information about actions, body language, graphics, and scene
          changes.
          
   Author styles
          Authors styles are style property values that come from content
          (e.g., style sheets within a document, that are associated with
          a document, or that are generated by a server).
          
   Captions
          Captions (sometimes, "closed captions") are text transcripts
          that are synchronized with other audio tracks or visual tracks.
          Captions convey information about spoken words and non-spoken
          sounds such as sound effects. They benefit people who are deaf
          or hard-of-hearing, and anyone who cannot hear the audio (e.g.,
          someone in a noisy environment). Captions are generally
          rendered graphically above, below, or superimposed over video.
          Note: Other terms that include the word "caption" may have
          different meanings in this document. For instance, a "table
          caption" is a title for the table, often positioned graphically
          above or below the table. In this document, the intended
          meaning of "caption" will be clear from context.
          
   Character encoding
          A "character encoding" is a mapping from a character set
          definition to the actual code units used to represent the data.
          Please refer to the Unicode specification [UNICODE] for more
          information about character encodings. Refer to "Character
          Model for the World Wide Web" [CHARMOD] for additional
          information about characters and character encodings.
          
   Collated text transcript
          A collated text transcript is a text equivalent of a movie or
          other animation. More specifically, it is the combination of
          the text transcript of the audio track and the text equivalent
          of the visual track. For example, a collated text transcript
          typically includes segments of spoken dialogue interspersed
          with text descriptions of the key visual elements of a
          presentation (actions, body language, graphics, and scene
          changes). See also the definitions of text transcript and
          auditory description. Collated text transcripts are essential
          for individuals who are deaf-blind.
          
   Conditional content
          Conditional content is content that, by format specification,
          should be made available to users through the user interface,
          generally under certain conditions (e.g., based on user
          preferences or operating environment limitations). Some
          examples of conditional content mechanisms include:
          
          + The "alt" attribute of the IMG element in HTML 4. According
            to section 13.2 of the HTML 4 specification ([HTML4]): "User
            agents must render alternate text when they cannot support
            images, they cannot support a certain image type or when they
            are configured not to display images.
          + OBJECT elements in HTML 4. Section 13.3.1 of the HTML 4
            specification ([HTML4]) explains the conditional rendering
            rules of (nested) OBJECT elements. The rules select among
            ordered alternatives according to user preferences or error
            conditions.
          + The switch element and test attributes in SMIL 1.0. Sections
            4.3 and 4.4, respectively, of SMIL 1.0 [SMIL] explain the
            conditional rendering rules of these features.
          + SVG 1.0 [SVG] also includes a switch element and several
            attributes for conditional processing.
          + The NOSCRIPT and NOFRAMES elements in HTML 4 [HTML4] allow
            the author to provide content under conditions when the user
            agent does not support scripts or frames, or the user has
            turned off support for scripts or frames.
            
          Specifications vary in how completely they define how and when
          to render conditional content. For instance, the HTML 4
          specification includes the rendering conditions for the "alt"
          attribute, but not for the "title" attribute. The HTML 4
          specification does indicate that the "title" attribute should
          be available to users through the user interface ("Values of
          the title attribute may be rendered by user agents in a variety
          of ways...").
          
          Note: The Web Content Accessibility Guidelines 1.0 requires
          that authors provide text equivalents for non-text content.
          This is generally done by using the conditional content
          mechanisms of a markup language. Since conditional content may
          not be rendered by default, the current document requires the
          user agent to provide access to unrendered conditional content
          (checkpoint 2.3 and checkpoint 2.9) as it may have been
          provided to promote accessibility.
          
   Configure, control
          In the context of this document, the verbs "to control" and "to
          configure" share in common the idea of governance such as a
          user may exercise over interface layout, user agent behavior,
          rendering style, and other parameters required by this
          document. Generally, the difference in the terms centers on the
          idea of persistence. When a user makes a change by
          "controlling" a setting, that change usually does not persist
          beyond that user session. On the other hand, when a user
          "configures" a setting, that setting typically persists into
          later user sessions. Furthermore, the term "control" typically
          means that the change can be made easily (such as through a
          keyboard shortcut) and that the results of the change occur
          immediately, whereas the term "configure" typically means that
          making the change requires more time and effort (such as making
          the change via a series of menus leading to a dialog box, via
          style sheets or scripts, etc.) and that the results of the
          change may not take effect immediately (e.g., due to time spent
          reinitializing the system, initiating a new session, rebooting
          the system). In order to be able to configure and control the
          user agent, the user needs to be able to "read" as well as
          "write" values for these parameters. Configuration settings may
          be stored in a profile. The range and granularity of the
          changes that can be controlled or configured by the user may
          depend on limitations of the operating environment or hardware.
          
          Both configuration and control may apply at different "levels":
          across Web resources (i.e., at the user agent level, or
          inherited from the operating environment), to the entirety of a
          Web resource, or to components of a Web resource (e.g., on a
          per-element basis).
          
          A global configuration is one that applies across elements of
          the same Web resource, as well as across Web resources. A
          global configuration may be implemented by more than one
          setting (e.g., per component of the user agent). For instance,
          when a user agent consists of a browser that renders HTML and a
          plug-in that renders SVG, to satisfy the global configuration
          requirements of this document, the browser may provide one
          setting and the plug-in another.
          
          User agents may allow users to choose configurations based on
          various parameters, such as hardware capabilities, natural
          language, etc.
          
          Note: In this document, the noun "control" refers to a
          component of the user agent user interface.
          
   Content
          In this specification, the noun "content" is used in three
          ways:
          
         1. It is used to mean the document object as a whole or in
            parts.
         2. It is used to mean the content of an HTML or XML element, in
            the sense employed by the XML 1.0 specification ([XML],
            section 3.1): "The text between the start-tag and end-tag is
            called the element's content." Context should indicate that
            the term content is being used in this sense.
         3. It is used in the context of the phrases non-text content and
            text content.
            
          Empty content is either a null value or a string consisting of
          zero characters. For instance, in HTML, "alt=''" sets the value
          of the "alt" attribute to the empty string. In some markup
          languages, an element may have empty content (e.g., the HR
          element in HTML).
          
   Device-independence
          Device-independence refers to the ability to make use of
          software with any appropriate supported input or output device.
          
   Document object, Document Object Model (DOM)
          In general usage, the term "document object" refers to the user
          agent's representation of data (e.g., a document). This data
          generally comes from the document source, but may also be
          generated (from style sheets, scripts, transformations, etc.),
          produced as a result of preferences set within the user agent,
          added as the result of a repair performed automatically by the
          user agent, etc. Some data that is part of the document object
          is routinely rendered (e.g., in HTML, what appears between the
          start and end tags of elements and the values of attributes
          such as "alt", "title", and "summary"). Other parts of the
          document object are generally processed by the user agent
          without user awareness, such as DTD- or schema-defined names of
          element types and attributes, and other attribute values such
          as "href", "id", etc. These guidelines require that users have
          access to both kinds of data through the user interface. Most
          of the requirements of this document apply to the document
          object after its construction. However, a few checkpoints
          (e.g., checkpoint 2.7 and checkpoint 2.11) may affect the
          construction of the document object.
          
          A "document object model" is the abstraction that governs the
          construction of the user agent's document object. The document
          object model employed by different user agents may vary in
          implementation and sometimes in scope. This specification
          requires that user agents implement the APIs defined in
          Document Object Model (DOM) Level 2 Specifications ([DOM2CORE]
          and [DOM2STYLE]) for access to HTML, XML, and CSS content.
          These DOM APIs allow authors to access and modify the content
          via a scripting language (e.g., JavaScript) in a consistent
          manner across different scripting languages. As a standard
          interface, the DOM APIs make it easier not just for authors,
          but for assistive technology developers to extract information
          and render it in ways most suited to the needs of particular
          users.
          
   Document character set
          A document character set (a concept taken from SGML) is a
          sequence of abstract characters that may appear in Web content
          represented in a particular format (such as HTML, XML, etc.). A
          document character set consists of:
          
          + a "repertoire", A set of abstract characters, such as the
            Latin letter "A", the Cyrillic letter "I", the Chinese
            character meaning "water", etc.
          + Code positions: A set of integer references to characters in
            the repertoire.
            
          For instance, the character set required by the HTML 4
          specification [HTML4] is defined in the Unicode specification
          [UNICODE]. Refer to "Character Model for the World Wide Web"
          [CHARMOD] for more information about document character sets.
          
   Document source, text source
          In this document, the term "document source" refers to the data
          that the user agent receives as the direct result of a request
          for a Web resource (e.g., as the result of an HTTP/1.1
          [RFC2616] "GET", or as the result of viewing a resource on the
          local file system). The document source generally refers to the
          "payload" of the user agent's request, and doesn't generally
          include information exchanged as part of the transfer protocol.
          The document source is data that is prior to any repair by the
          user agent (e.g., prior to repairing invalid markup). "Text
          source" refers to document source that is composed of text.
          
   Documentation
          Documentation refers to information that supports the use of a
          user agent. This information may be found in manuals,
          installation instructions, the help system, tutorials, etc.
          Documentation may be distributed (e.g., some parts may be
          delivered on CD-ROM, others on the Web). Refer to guideline 12
          for information about documentation requirements.
          
   Element, element type,
          This document uses the terms "element" and "element type" in
          the sense employed by the XML 1.0 specification ([XML], section
          3): an element type is a syntactic construct of a Document Type
          Definition (DTD) for its application. This sense is also
          relevant to structures defined by XML schemas. The document
          also uses the term "element" more generally to mean a type of
          content (such as video or sound) or a logical construct (such
          as a header or list).
          
   Enabled element, disabled element
          An enabled element is a piece of content with associated
          behaviors that may be activated through the user interface or
          through an API. The set of elements that a user agent enables
          is generally derived from, but is not limited to, the set of
          interactive elements defined by implemented markup languages.
          
          Some elements may only be enabled elements for part of a user
          session. For instance, an element may be disabled by a script
          as the result of user interaction. Or, an element may only be
          enabled during a given time period (e.g., during part of a SMIL
          1.0 [SMIL] presentation). Or, the user may be viewing content
          in "read-only" mode, which may disable some elements.
          
          A disabled element is a piece of content that is potentially an
          enabled element, but is not in the current session. Generally,
          disabled elements will be interactive elements that are not
          enabled in the current session. This document distinguishes
          disabled elements (not currently enabled) from non-interactive
          elements (never enabled).
          
          For the requirements of this document, user selection does not
          constitute user interaction with enabled elements. See the
          definition of content focus.
          
          Note: Enabled and disabled elements come from content; they are
          not part of the user agent user interface.
          
          Note: The term "active element" is not used in this document
          since it may suggest several different concepts, including:
          interactive element, enabled element, an element "in the
          process of being activated" (which is the meaning of ':active'
          in CSS2 [CSS2], for example).
          
   Equivalent (for content)
          The term "equivalent" is used in this document as it is used in
          the Web Content Accessibility Guidelines 1.0 [WCAG10]:
          
     Content is "equivalent" to other content when both fulfill
     essentially the same function or purpose upon presentation to the
     user. In the context of this document, the equivalent must fulfill
     essentially the same function for the person with a disability (at
     least insofar as is feasible, given the nature of the disability
     and the state of technology), as the primary content does for the
     person without any disability.
     
          Equivalents include text equivalents (e.g., text equivalents
          for images; text transcripts for audio tracks; collated text
          transcripts for multimedia presentations and animations) and
          non-text equivalents (e.g., a prerecorded auditory description
          of a visual track of a movie, or a sign language video
          rendition of a written text, etc.).
          
          Each markup language defines its own mechanisms for specifying
          conditional content, and these mechanisms may be used by
          authors to provide text equivalents. For instance, in HTML 4
          [HTML4] or SMIL 1.0 [SMIL], authors may use the "alt" attribute
          to specify a text equivalent for some elements. In HTML 4,
          authors may provide equivalents (or portions of equivalents) in
          attribute values (e.g., the "summary" attribute for the TABLE
          element), in element content (e.g., OBJECT for external content
          it specifies, NOFRAMES for frame equivalents, and NOSCRIPT for
          script equivalents), and in prose. Please consult the Web
          Content Accessibility Guidelines 1.0 [WCAG10] and its
          associated Techniques document [WCAG10-TECHS] for more
          information about equivalents.
          
   Events and scripting, event handler
          User agents often perform a task when an event occurs that is
          due to user interaction (e.g., document loading, mouse motion
          or a key press, a request from the operating environment,
          etc.). Some markup languages allow authors to specify that a
          script, called an event handler, be executed when the event
          occurs. An event handler is "explicitly associated with an
          element" when the event handler is associated with that element
          through markup or the DOM. The term "event bubbling" describes
          a programming style where a single event handler dispatches
          events to more than one element. In this case, the event
          handlers are not explicitly associated with the elements
          receiving the events (except for the single element that
          dispatches the events).
          
          Note: The combination of HTML, style sheets, the Document
          Object Model (DOM) and scripting is commonly referred to as
          "Dynamic HTML" or DHTML. However, as there is no W3C
          specification that formally defines DHTML, this document only
          refers to event handlers and scripts.
          
   Explicit user request
          In this document, the term "explicit user request" refers to
          any user interaction with a control provided by the user agent
          user interface (not those in content), the focus, or selection.
          Control behavior should be documented.
          
          Some examples of explicit user requests include when the user
          selects "New viewport", responds "Yes" to a prompt in the user
          agent's user interface, configures the user agent to behave in
          a certain way, or changes the selection or focus with the
          keyboard or pointing device.
          
          Note: Users make mistakes. For example, a user may
          inadvertently respond "yes" to a prompt when they meant "no."
          In this document, this type of mistake is still considered an
          explicit user request.
          
   Fee link
          For the purpose of this document, the term "fee link" refers to
          a link that when activated, debits the user's electronic
          "wallet" (generally, a "micropayment"). The link's role as a
          fee link is identified through markup (in a manner that the
          user agent can recognize). This definition of fee link excludes
          payment mechanisms (e.g., some form-based credit card
          transactions) that cannot be recognized by the user agent as
          causing payments. For more information about fee links, refer
          to "Common Markup for micropayment per-fee-links"
          [MICROPAYMENT].
          
   Focus, content focus, user interface focus, current focus
          In this document, the term "content focus" refers to a user
          agent mechanism that satisfies all of the following properties:
          
         1. It designates zero or one element in content that is either
            enabled or disabled. (In general, the focus should only
            designate enabled elements, but it may also designate
            disabled elements.)
         2. The user may "set" content focus (programmatically or through
            the user interface) on an enabled element without triggering
            the associated behaviors.
         3. It has state. The user may prefer to always move the content
            focus manually from one element to another.
         4. It may be used (programmatically or through the user
            interface) to trigger the behaviors associated with an
            enabled element. This is generally implemented by making the
            focus respond to input device events (often just keyboard
            events).
            
          User interface mechanisms may resemble content focus, but do
          not satisfy all of the properties. For example, text editors
          often implement a "caret" that indicates the current location
          of text input or editing. The caret may have state and may
          respond to input device events, but it does not enable users to
          activate the behaviors associated with enabled elements.
          
          The user interface focus shares the properties of the content
          focus except the first: the user interface focus designates
          zero or one control of the user agent user interface that has
          associated behaviors (e.g., radio button, text box, menu,
          etc.).
          
          On the screen, the content focus may be highlighted using
          colors, fonts, graphics, magnification, etc. The content focus
          may also be highlighted when rendered as synthesized speech,
          for example through changes in speech prosody. The dimensions
          of the rendered content focus may exceed those of the viewport.
          
          In this document, each viewport is expected to have at most one
          content focus and at most one user interface focus. This
          document includes requirements for content focus only, for user
          interface focus only, and for both. When a requirement refers
          to both, the term "focus" is used.
          
          When several viewports coexist, at most one viewport's content
          focus or user interface focus responds to input events; this is
          called the current focus.
          
   Graphical
          In this document, the term "graphical" refers to information
          (text, colors, graphics, images, animations, etc.) rendered for
          visual consumption.
          
   Highlight
          In this document, "to highlight" means to emphasize through the
          user interface. For example, user agents highlight which
          content is selected or focused. Graphical highlight mechanisms
          include dotted boxes, underlining, and reverse video.
          Synthesized speech highlight mechanisms include alterations of
          voice pitch and volume ("speech prosody").
          
   Image
          In this document, an "image" refers to content that encodes
          static (i.e., unmoving) visual information. See also the
          definition of animation.
          
   Input configuration
          An input configuration is the mapping of user agent
          functionalities to some user interface input mechanisms (e.g.,
          menus, buttons, keyboard keys, voice commands, etc.). The
          default input configuration is the mapping the user finds after
          installation of the software; it must be documented (per
          checkpoint 12.3]). Input configurations may be affected by
          author-specified bindings (e.g., through the "accesskey"
          attribute of HTML 4 [HTML4]).
          
   Interactive element, non-interactive element,
          An interactive element is piece of content that, by
          specification, may have associated behaviors to be executed or
          carried out as a result of user or programmatic interaction.
          For instance, the interactive elements of HTML 4 [HTML4]
          include: links, image maps, form elements, elements with a
          value for the "longdesc" attribute, and elements with event
          handlers explicitly associated with them (e.g., through the
          various "on" attributes). The role of an element as an
          interactive element is subject to applicability. A
          non-interactive element is an element that, by format
          specification, does not have associated behaviors. The
          expectation of this document is that interactive elements
          become enabled elements in some sessions, and non-interactive
          elements never become enabled elements.
          
   Natural language
          Natural language is spoken, written, or signed human language
          such as French, Japanese, and American Sign Language. On the
          Web, the natural language of content may be specified by markup
          or HTTP headers. Some examples include the "lang" attribute in
          HTML 4 ([HTML4] section 8.1), the "xml:lang" attribute in XML
          1.0 ([XML], section 2.12), the HTML 4 "hreflang" attribute for
          links in HTML 4 ([HTML4], section 12.1.5), the HTTP
          Content-Language header ([RFC2616], section 14.12) and the
          Accept-Language request header ([RFC2616], section 14.4). See
          also the definition of script.
          
   Normative, informative
          As used in this document, the term "normative" refers to "that
          on which the requirements of this document depend for their
          most precise statement." What is normative is required for
          conformance (though the conformance scheme of this document
          allows claimants to exempt certain normative provisions as long
          as the claim discloses the exemption). What is identified as
          "informative" (sometimes, "non-normative") is never required
          for conformance.
          
   Operating environment
          The term "operating environment" refers to the environment that
          governs the user agent's operation, whether it is an operating
          system or a programming language environment such as Java.
          
   Override
          In this document, the term "override" means that one
          configuration or behavior preference prevails over another.
          Generally, the requirements of this document involve user
          preferences prevailing over author preferences and user agent
          default settings and behaviors. Preferences may be multi-valued
          in general (e.g., the user prefers blue over red or yellow),
          and include the special case of two values (e.g., turn on or
          off blinking text content).
          
   Placeholder
          A placeholder is content generated by the user agent to replace
          author-supplied content. A placeholder may be generated as the
          result of a user preference (e.g., to not render images) or as
          repair content (e.g., when an image cannot be found).
          Placeholders can be any type of content, including text,
          images, and audio cues.
          
          This document includes requirements that the user be able to
          view the original author-supplied content associated with a
          placeholder. To satisfy these requirements, the user agent
          might render the content in place of the placeholder or in a
          separate viewport (leaving the placeholder as is). A request to
          view the original content associated with a placeholder is
          considered an explicit user request to render that content.
          
          This document does not require user agents to include
          placeholders in the document object. A placeholder that is
          inserted in the document object should conform to the Web
          Content Accessibility Guidelines 1.0 [WCAG10]. If a placeholder
          is not part of the document object, it is part of the user
          interface only (and subject, for example, to checkpoint 1.3).
          
   Plug-in
          A plug-in is a program that runs as part of the user agent and
          that is not part of content. Users generally choose to include
          or exclude plug-ins from their user agent.
          
   Point of regard
          The point of regard is a position in rendered content that the
          user is presumed to be viewing. The dimensions of the point of
          regard may vary. For example, it may be a point (e.g., a moment
          in an audio rendering or a cursor in a graphical rendering), or
          a range of text (e.g., focused text), or a two-dimensional area
          (e.g., content rendered through a two-dimensional graphical
          viewport). The point of regard is almost always within the
          viewport, but it may exceed the spatial or temporal dimensions
          of the viewport (see the definition of rendered content for
          more information about viewport dimensions). The point of
          regard may also refer to a particular moment in time for
          content that changes over time (e.g., an audio-only
          presentation). User agents may determine the point of regard in
          a number of ways, including based on viewport position in
          content, content focus, selection, etc. A user agent should not
          change the point of regard unexpectedly as this may disorient
          the user.
          
   Profile
          A profile is a named and persistent representation of user
          preferences that may be used to configure a user agent.
          Preferences include input configurations, style preferences,
          natural language preferences, etc. In operating environments
          with distinct user accounts, profiles enable users to
          reconfigure software quickly when they log on, and profiles may
          be shared by several users. Platform-independent profiles are
          useful for those who use the same user agent on different
          platforms.
          
   Prompt
          In this document, "to prompt" means to require input from the
          user. The user agent should allow users to configure how they
          wish to be prompted. For instance, for a user agent
          functionality X, configurations might include: always prompt me
          before doing X, always do X without prompting me, never do X
          but tell me when you could have, never do X and never tell me
          that you could have, etc.
          
   Properties, values, and defaults
          A user agent renders a document by applying formatting
          algorithms and style information to the document's elements.
          Formatting depends on a number of factors, including where the
          document is rendered: on screen, on paper, through
          loudspeakers, on a braille display, on a mobile device, etc.
          Style information (e.g., fonts, colors, synthesized speech
          prosody, etc.) may come from the elements themselves (e.g.,
          certain font and phrase elements in HTML), from style sheets,
          or from user agent settings. For the purposes of these
          guidelines, each formatting or style option is governed by a
          property and each property may take one value from a set of
          legal values. Generally in this document, the term "property"
          has the meaning defined in CSS 2 ([CSS2], section 3). A
          reference to "styles" in this document means a set of
          style-related properties.
          The value given to a property by a user agent when it is
          installed is called the property's default value.
          
   Recognize
          Authors encode information in markup languages, style sheet
          languages, scripting languages, protocols, etc. When the
          information is encoded in a manner that allows the user agent
          to process it with certainty, the user agent can "recognize"
          the information. For instance, HTML allows authors to specify a
          heading with the H1 element, so a user agent that implements
          HTML can recognize that content as a heading. If the author
          creates headings using a visual effect alone (e.g., by
          increasing the font size), then the author has encoded the
          heading in a manner that does not allow the user agent to
          recognize it as a heading.
          
          Some requirements of this document depend on content roles,
          content relationships, timing relationships, and other
          information supplied by the author. These requirements only
          apply when the author has encoded that information in a manner
          that the user agent can recognize. See the section on
          conformance for more information about applicability.
          
          In practice, user agents will rely heavily on information that
          the author has encoded in a markup language or style sheet
          language. On the other hand, behaviors, style, meaning encoded
          in a script, and markup in an unfamiliar XML namespace may not
          be recognized by the user agent as easily or at all. The
          Techniques document [UAAG10-TECHS] lists some markup known to
          affect accessibility that user agents can recognize.
          
   Rendered content, rendered text
          Rendered content is the part of content that the user agent
          makes available to the user's senses of sight and hearing (and
          only those senses for the purposes of this document). Any
          content that causes an effect that may be perceived through
          these senses constitutes rendered content. This includes text
          characters, images, style sheets, scripts, and anything else in
          content that, once processed, may be perceived through sight
          and hearing.
          
          The term "rendered text" refers to text content that is
          rendered in a way that communicates information about the
          characters themselves, whether visually or as synthesized
          speech.
          
          In the context of this document, "invisible content" is content
          that influences graphical rendering of other content but is not
          rendered itself. Similarly, "silent content" is content that
          influences audio rendering of other content but is not rendered
          itself. Neither invisible nor silent content is considered
          rendered content.
          
   Repair content, repair text
          In this document, the term "repair content" refers to content
          generated by the user agent in order to correct an error
          condition. "Repair text" means repair content consisting only
          of text. Some error conditions that may lead to the generation
          of repair content include:
          
          + Erroneous or incomplete content (e.g., ill-formed markup,
            invalid markup, missing conditional content that is required
            by format specification, etc.);
          + Missing resources for handling or rendering content (e.g.,
            the user agent lacks a font family to display some
            characters, the user agent doesn't implement a particular
            scripting language, etc.);
            
          This document does not require user agents to include repair
          content in the document object. Repair content inserted in the
          document object should conform to the Web Content Accessibility
          Guidelines 1.0 [WCAG10]. For more information about repair
          techniques for Web content and software, refer to "Techniques
          for Authoring Tool Accessibility Guidelines 1.0"
          [ATAG10-TECHS].
          
   Script
          In this document, the term "script" almost always refers to a
          scripting (programming) language used to create dynamic Web
          content. However, in checkpoints referring to the written
          (natural) language of content, the term "script" is used as in
          Unicode [UNICODE] to mean "A collection of symbols used to
          represent textual information in one or more writing systems."
          
          Information encoded in scripts may be difficult for a user
          agent to recognize For instance, a user agent is not expected
          to recognize that, when executed, a script will calculate a
          factorial. The user agent will be able to recognize some
          information in a script by virtue of implementing the scripting
          language or a known program library (e.g., the user agent is
          expected to recognize when a script will open a viewport or
          retrieve a resource from the Web).
          
   Selection, current selection
          In this document, the term "selection" refers to a user agent
          mechanism for identifying a range of content (e.g., text,
          images, etc.). Generally, user agents limit selection to text
          content (e.g., one or more fragments of text). The selection
          may be structured (based on the document tree) or unstructured
          (e.g., text-based). The range may be empty.
          
          On the screen, the selection may be highlighted using colors,
          fonts, graphics, magnification, etc. The selection may also be
          highlighted when rendered as synthesized speech, for example
          through changes in speech prosody. The dimensions of the
          rendered selection may exceed those of the viewport.
          
          The selection may be used for a variety of purposes: for cut
          and paste operations, to designate a specific element in a
          document for the purposes of a query, as an indication of point
          of regard, etc.
          
          The selection has state. It may be set programmatically or
          through the user interface.
          
          In this document, each viewport is expected to have at most one
          selection. When several viewports coexist, at most one
          viewport's selection responds to input events; this is called
          the current selection.
          
          See the section on the selection label for information about
          implementing a selection and conformance.
          
          Note: Some user agents may also implement a selection for
          designating a range of information in controls of the user
          agent user interface. The current document only includes
          requirements for a content selection mechanism.
          
   Support, implement, conform
          In this document, the terms "support", "implement", and
          "conform" all refer to what a developer has designed a user
          agent to do, but they represent different degrees of
          specificity. A user agent "supports" general classes of
          objects, such as "images" or "Japanese". A user agent
          "implements" a specification (e.g., the PNG and SVG image
          format specifications, a particular scripting language, etc.)
          or an API (e.g., the DOM API) when it has been programmed to
          follow all or part of a specification. A user agent "conforms
          to" a specification when it implements the specification and
          satisfies its conformance criteria. This document includes some
          conformance requirements to other specifications (e.g., to a
          particular level of the "Web Content Accessibility Guidelines
          1.0" [WCAG10]).
          
   Synchronize
          In this document, "to synchronize" refers to the
          time-coordination of two or more presentation components (e.g.,
          in a multimedia presentation, a visual track with captions).
          For Web content developers, the requirement to synchronize
          means to provide the data that will permit sensible
          time-coordinated rendering by a user agent. For example, Web
          content developers can ensure that the segments of caption text
          are neither too long nor too short, and that they map to
          segments of the visual track that are appropriate in length.
          For user agent developers, the requirement to synchronize means
          to present the content in a sensible time-coordinated fashion
          under a wide range of circumstances including technology
          constraints (e.g., small text-only displays), user limitations
          (slow reading speeds, large font sizes, high need for review or
          repeat functions), and content that is sub-optimal in terms of
          accessibility.
          
   Text
          In this document, the term "text" used by itself refers to a
          sequence of characters from a markup language's document
          character set. Refer to the "Character Model for the World Wide
          Web " [CHARMOD] for more information about text and characters.
          Note: This document makes use of other terms that include the
          word "text" that have highly specialized meanings: collated
          text transcript, non-text content, text content, non-text
          element, text element, text equivalent, and text transcript.
          
   Text content, non-text content, text element, non-text element, text
          equivalent non-text equivalent
          As used in this document a "text element" adds text characters
          to either content or the user interface. Both in the Web
          Content Accessibility Guidelines 1.0 [WCAG10] and in this
          document, text elements are presumed to produce text that can
          be understood when rendered visually, as synthesized speech, or
          as Braille. Such text elements benefit at least these three
          groups of users:
          
         1. visually-displayed text benefits users who are deaf and adept
            in reading visually-displayed text;
         2. synthesized speech benefits users who are blind and adept in
            use of synthesized speech;
         3. braille benefits users who are blind, and possibly
            deaf-blind, and adept at reading braille.
            
          A text element may consist of both text and non-text data. For
          instance, a text element may contain markup for style (e.g.,
          font size or color), structure (e.g., heading levels), and
          other semantics. The essential function of the text element
          should be retained even if style information happens to be lost
          in rendering.
          
          A user agent may have to process a text element in order to
          have access to the text characters. For instance, a text
          element may consist of markup, it may be encrypted or
          compressed, or it may include embedded text in a binary format
          (e.g., JPEG).
          
          "Text content" is content that is composed of one or more text
          elements. A "text equivalent" (whether in content or the user
          interface) is an equivalent composed of one or more text
          elements. Authors generally provide text equivalents for
          content by using the conditional content mechanisms of a
          specification.
          
          A "non-text element" is an element (in content or the user
          interface) that does not have the qualities of a text element.
          "Non-text content" is composed of one or more non-text
          elements. A "non-text equivalent" (whether in content or the
          user interface) is an equivalent composed of one or more
          non-text elements.
          
          Note that the terms "text element" and "non-text element" are
          defined by the characteristics of their output (e.g.,
          rendering) rather than those of their input (e.g., information
          sources) or their internals (e.g., format). Both text elements
          and non-text elements should be understood as "pre-rendering"
          content in contrast to the "post-rendering" content that they
          produce.
          
   Text decoration
          In this document, a "text decoration" is any stylistic effect
          that the user agent may apply to visually rendered text that
          does not affect the layout of the document (i.e., does not
          require reformatting when applied or removed). Text decoration
          mechanisms include underline, overline, and strike-through.
          
   Text transcript
          A text transcript is a text equivalent of audio information
          (e.g., an audio-only presentation or the audio track of a movie
          or other animation). It provides text for both spoken words and
          non-spoken sounds such as sound effects. Text transcripts make
          audio information accessible to people who have hearing
          disabilities and to people who cannot play the audio. Text
          transcripts are usually pre-written but may be generated on the
          fly (e.g., by voice-to-text converters). See also the
          definitions of captions and collated text transcripts.
          
   User agent
          In this document, the term "user agent" is used in two ways:
          
         1. 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.
         2. The subject of a conformance claim to this document. This is
            the most common use of the term in this document and is the
            usage in the checkpoints.
            
   User agent default styles
          User agent default styles are style property values applied in
          the absence of any author or user styles. Some markup languages
          specify a default rendering for documents in that markup
          language. Other specifications may not specify default styles.
          For example, XML 1.0 [XML] does not specify default styles for
          XML documents. HTML 4 [HTML4] does not specify default styles
          for HTML documents, but the CSS 2 [CSS2] specification suggests
          a sample default style sheet for HTML 4 based on current
          practice.
          
   User interface
          For the purposes of this document, user interface includes
          both:
          
         1. the "user agent user interface", i.e., the controls (e.g.,
            menus, buttons, prompts, etc.) and mechanisms (e.g.,
            selection and focus) provided by the user agent ("out of the
            box") that are not created by content.
         2. the "content user interface", i.e., the enabled elements that
            are part of content, such as form elements, links, applets,
            etc.
            
          The document distinguishes them only where required for
          clarity.
          
   User styles
          User styles are style property values that come from user
          interface settings, user style sheets, or other user
          interactions.
          
   Visual-only presentation
          A visual-only presentation is content consisting exclusively of
          one or more visual tracks presented concurrently or in series.
          A silent movie is an example of a visual-only presentation.
          
   Visual track
          A visual object is content rendered through a graphical
          viewport. Visual objects include graphics, text, and visual
          portions of movies and other animations. A visual track is a
          visual object that is intended as a whole or partial
          presentation. A visual track does not necessarily correspond to
          a single physical object or software object. A visual track may
          be text-based or graphic. A visual track may be static or
          involve animation.
          
   Views, viewports
          The user agent renders content through one or more viewports.
          Viewports include windows, frames, pieces of paper,
          loudspeakers, virtual magnifying glasses, etc. A viewport may
          contain another viewport (e.g., nested frames). User interface
          controls such as prompts, menus, alerts, etc. are not
          viewports.
          
          When the dimensions (spatial or temporal) of rendered content
          exceed the dimensions of the viewport (e.g., when the user can
          only view a portion of a large document through a small
          graphical viewport, when audio content has already been played,
          etc.), the user agent provides mechanisms such as scroll bars
          and advance and rewind controls so that the user can access the
          rendered content "outside" the viewport.
          
          When several viewports coexist, only one has the current focus
          at a given moment. This viewport is highlighted to make it
          stand out.
          
          User agents may render the same content in a variety of ways;
          each rendering is called a view. For instance, a user agent may
          allow users to view an entire document or just a list of the
          document's headers. These are two different views of the
          document.
          
   Voice browser
          From "Introduction and Overview of W3C Speech Interface
          Framework" [VOICEBROWSER]: "A voice browser is a device
          (hardware and software) that interprets voice markup languages
          to generate voice output, interpret voice input, and possibly
          accept and produce other modalities of input and output."
          
   Web resource
          The term "Web resource" is used in this document in accordance
          with Web Characterization Terminology and Definitions Sheet
          [WEBCHAR] to mean anything that can be identified by a Uniform
          Resource Identifier (URI); refer to RFC 2396 [RFC2396].
          
5. References

   For the latest version of any W3C specification please consult the
   list of W3C Technical Reports at http://www.w3.org/TR/. Some documents
   listed below may have been superseded since the publication of this
   document.
   
   Note: In this document, bracketed labels such as "[HTML4]" link to the
   corresponding entries in this section. These labels are also
   identified as references through markup.
   
  5.1 How to refer to this document
  
   There are two recommended ways to refer to the "User Agent
   Accessibility Guidelines 1.0" (and to W3C documents in general):
    1. References to a specific version of "User Agent Accessibility
       Guidelines 1.0". For example, use the "this version" URI to refer
       to the current document:
       http://www.w3.org/TR/2001/CR-UAAG10-20010912/.
    2. References to the latest version of "User Agent Accessibility
       Guidelines 1.0". Use the "latest version" URI to refer to the most
       recently published document in the series:
       http://www.w3.org/TR/UAAG10/.
       
   In almost all cases, references (either by name or by link) should be
   to a specific version of the document. W3C will make every effort to
   make this document indefinitely available at its original address in
   its original form. The top of this document includes the relevant
   catalog metadata for specific references (including title, publication
   date, "this version" URI, editors' names, and copyright information).
   
   An XHTML 1.0 [XHTML10] paragraph including a reference to this
   specific document might be written:
<p>
<cite><a href="http://www.w3.org/TR/2001/CR-UAAG10-20010912/">
"User Agent Accessibility Guidelines 1.0"</a></cite>,
I. Jacobs, J. Gunderson, E. Hansen, eds.,
W3C Candidate Recommendation, 12 September 2001.
The <a href="http://www.w3.org/TR/UAAG10/">latest
version</a> of this document is available at
http://www.w3.org/TR/UAAG10/.</p>

   For very general references to this document (where stability of
   content, anchors, etc., is not required), it may be appropriate to
   refer to the latest version of this document. In this case, please use
   the "latest version" URI at the top of this document.
   
   See also information about making conformance claims to this document.
   
  5.2 Normative references
  
   [CSS1]
          "CSS, level 1 Recommendation", B. Bos, H. Wium Lie, eds., 17
          December 1996, revised 11 January 1999. This W3C Recommendation
          is http://www.w3.org/TR/1999/REC-CSS1-19990111.
          
   [CSS2]
          "CSS, level 2 Recommendation", B. Bos, H. Wium Lie, C. Lilley,
          and I. Jacobs, eds., 12 May 1998. This W3C Recommendation is
          http://www.w3.org/TR/1998/REC-CSS2-19980512/.
          
   [DOM2CORE]
          "Document Object Model (DOM) Level 2 Core Specification", A. Le
          Hors, P. Le Hégaret, L. Wood, G. Nicol, J. Robie, M. Champion,
          S. Byrne, eds., 13 November 2000. This W3C Recommendation is
          http://www.w3.org/TR/2000/REC-DOM-Level-2-Core-20001113/.
          
   [DOM2STYLE]
          "Document Object Model (DOM) Level 2 Style Specification", V.
          Apparao, P. Le Hégaret, C. Wilson, eds., 13 November 2000. This
          W3C Recommendation is
          http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/.
          
   [RFC2046]
          "Multipurpose Internet Mail Extensions (MIME) Part Two: Media
          Types", N. Freed, N. Borenstein, November 1996.
          
   [RFC2119]
          "Key words for use in RFCs to Indicate Requirement Levels", S.
          Bradner, March 1997.
          
   [WCAG10]
          "Web Content Accessibility Guidelines 1.0", W. Chisholm, G.
          Vanderheiden, and I. Jacobs, eds., 5 May 1999. This W3C
          Recommendation is
          http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/.
          
  5.3 Informative references
  
   Some of the references in this section become normative if they are
   used to satisfy the requirements of guideline 6 and guideline 8.
   
   [AT1998]
          The Assistive Technology Act of 1998, 13 November 1998, United
          States P.L. 105-394.
          
   [ATAG10]
          "Authoring Tool Accessibility Guidelines 1.0", J. Treviranus,
          C. McCathieNevile, I. Jacobs, and J. Richards, eds., 3 February
          2000. This W3C Recommendation is
          http://www.w3.org/TR/2000/REC-ATAG10-20000203/.
          
   [ATAG10-TECHS]
          "Techniques for Authoring Tool Accessibility Guidelines 1.0",
          J. Treviranus, C. McCathieNevile, I. Jacobs, and J. Richards,
          eds., 4 May 2000. This W3C Note is
          http://www.w3.org/TR/2000/NOTE-ATAG10-TECHS-20000504/.
          
   [CHARMOD]
          "Character Model for the World Wide Web", M. Dürst and F.
          Yergeau, eds., 29 November 1999. This W3C Working Draft is
          http://www.w3.org/TR/1999/WD-charmod-19991129/
          
   [HTML4]
          "HTML 4.01 Recommendation", D. Raggett, A. Le Hors, and I.
          Jacobs, eds., 24 December 1999. This W3C Recommendation is
          http://www.w3.org/TR/1999/REC-html401-19991224/.
          
   [MATHML20]
          "Mathematical Markup Language (MathML) Version 2.0", D.
          Carlisle, P. Ion, R. Miner, N. Poppelier, et al., 21 February
          2001. This W3C Recommendation is
          http://www.w3.org/TR/2001/REC-MathML2-20010221/.
          
   [MICROPAYMENT]
          "Common Markup for micropayment per-fee-links", T. Michel, ed.,
          25 August 1999. This W3C Working Draft is
          http://www.w3.org/TR/1999/WD-Micropayment-Markup-19990825/.
          
   [PNG]
          "PNG (Portable Network Graphics) Specification 1.0", T.
          Boutell, ed., 1 October 1996. This W3C Recommendation is
          http://www.w3.org/TR/REC-png.
          
   [RDF10]
          "Resource Description Framework (RDF) Model and Syntax
          Specification", O. Lassila, R. Swick, eds., 22 February 1999.
          This W3C Recommendation is
          http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/.
          
   [RFC2396]
          "Uniform Resource Identifiers (URI): Generic Syntax", T.
          Berners-Lee, R. Fielding, L. Masinter, August 1998.
          
   [RFC2616]
          "Hypertext Transfer Protocol -- HTTP/1.1", J. Gettys, J. Mogul,
          H. Frystyk, L. Masinter, P. Leach, T. Berners-Lee, June 1999.
          
   [SMIL]
          "Synchronized Multimedia Integration Language (SMIL) 1.0
          Specification", P. Hoschka, ed., 15 June 1998. This W3C
          Recommendation is http://www.w3.org/TR/1998/REC-smil-19980615/.
          
   [SMIL20]
          Synchronized Multimedia Integration Language (SMIL 2.0)
          Specification, J. Ayars, et al., eds., 7 August 2001. This W3C
          Recommendation is
          http://www.w3.org/TR/2001/REC-smil20-20010807/.
          
   [SVG]
          "Scalable Vector Graphics (SVG) 1.0 Specification", J.
          Ferraiolo, ed., 2 August 2000. This W3C Candidate
          Recommendation is http://www.w3.org/TR/2000/CR-SVG-20000802/.
          
   [UAAG10-CHECKLIST]
          An appendix to this document lists all of the checkpoints,
          sorted by priority. The checklist is available in either
          tabular form or list form.
          
   [UAAG10-SUMMARY]
          An appendix to this document provides a summary of the goals
          and structure of User Agent Accessibility Guidelines 1.0.
          
   [UAAG10-TECHS]
          "Techniques for User Agent Accessibility Guidelines 1.0", I.
          Jacobs, J. Gunderson, E. Hansen, eds. The latest draft of the
          techniques document is available at
          http://www.w3.org/TR/UAAG10-TECHS/.
          
   [UNICODE]
          "The Unicode Standard, Version 3.1". This technical report of
          the Unicode Consortium is available at
          http://www.unicode.org/unicode/reports/tr27/. This is a
          revision of "The Unicode Standard, Version 3.0", The Unicode
          Consortium, Addison-Wesley Developers Press, 2000. ISBN
          0-201-61633-5. Refer also to
          http://www.unicode.org/unicode/standard/versions/. For
          information about character encodings, refer to Unicode
          Technical Report #17 "Character Encoding Model".
          
   [VOICEBROWSER]
          "Voice Browsers: An introduction and glossary for the
          requirements drafts", M. Robin, J. Larson, 23 December 1999.
          This document is
          http://www.w3.org/TR/1999/WD-voice-intro-19991223/. This
          document includes references to additional W3C specifications
          about voice browser technology.
          
   [W3CPROCESS]
          "World Wide Web Consortium Process Document", I. Jacobs ed. The
          11 November 1999 version of the Process Document is
          http://www.w3.org/Consortium/Process/Process-19991111/.
          
   [WCAG10-TECHS]
          "Techniques for Web Content Accessibility Guidelines 1.0", W.
          Chisholm, G. Vanderheiden, and I. Jacobs, eds. This W3C Note is
          http://www.w3.org/TR/1999/WAI-WEBCONTENT-TECHS-19990505/.
          
   [WEBCHAR]
          "Web Characterization Terminology and Definitions Sheet", B.
          Lavoie, H. F. Nielsen, eds., 24 May 1999. This is a W3C Working
          Draft that defines some terms to establish a common
          understanding about key Web concepts. This W3C Working Draft is
          http://www.w3.org/1999/05/WCA-terms/01.
          
   [XHTML10]
          "XHTML[tm] 1.0: The Extensible HyperText Markup Language", S.
          Pemberton, et al., 26 January 2000. This W3C Recommendation is
          http://www.w3.org/TR/2000/REC-xhtml1-20000126/.
          
   [XML]
          "Extensible Markup Language (XML) 1.0", T. Bray, J. Paoli, C.M.
          Sperberg-McQueen, eds., 10 February 1998. This W3C
          Recommendation is http://www.w3.org/TR/1998/REC-xml-19980210.
          
6. Acknowledgments

   The active participants of the User Agent Accessibility Guidelines
   Working Group who authored this document were: James Allan, Denis
   Anson (College Misericordia), Harvey Bingham, Al Gilman, Jon Gunderson
   (Chair of the Working Group, University of Illinois,
   Urbana-Champaign), Eric Hansen (Educational Testing Service), Ian
   Jacobs (Team Contact, W3C), Tim Lacy (Microsoft), Charles
   McCathieNevile (W3C), David Poehlman, Mickey Quenzer, Gregory Rosmaita
   (Visually Impaired Computer Users Group of New York City), and Rich
   Schwerdtfeger (IBM).
   
   Many thanks to the following people who have contributed through
   review and past participation in the Working Group: Paul Adelson,
   Jonny Axelsson, Kitch Barnicle, Olivier Borius, Judy Brewer, Dick
   Brown, Bryan Campbell, Kevin Carey, Tantek Çelik, Wendy Chisholm,
   David Clark, Chetz Colwell, Wilson Craig, Nir Dagan, Daniel
   Dardailler, B. K. Delong, Neal Ewers, Geoff Freed, John Gardner, Larry
   Goldberg, Glen Gordon, John Grotting, Markku Hakkinen, Earle Harrison,
   Chris Hasser, Kathy Hewitt, Philipp Hoschka, Masayasu Ishikawa, Phill
   Jenkins, Earl Johnson, Jan Kärrman (for help with html2ps), Leonard
   Kasday, George Kerscher, Marja-Riitta Koivunen, Peter Korn, Josh
   Krieger, Catherine Laws, Aaron Leventhal, Greg Lowney, Susan Lesch,
   Scott Luebking, William Loughborough, Napoleon Maou, Peter Meijer,
   Karen Moses, Masafumi Nakane, Mark Novak, Charles Oppermann, Mike
   Paciello, David Pawson, Michael Pederson, Helen Petrie, Michael
   Pieper, Richard Premack, Jan Richards, Hans Riesebos, Joe Roeder,
   Lakespur L. Roca, Madeleine Rothberg, Lloyd Rutledge, Liam Quinn, T.V.
   Raman, Robert Savellis, Constantine Stephanidis, Jim Thatcher, Jutta
   Treviranus, Claus Thogersen, Steve Tyler, Gregg Vanderheiden, Jaap van
   Lelieveld, Jon S. von Tetzchner, Willie Walker, Ben Weiss, Evan Wies,
   Chris Wilson, Henk Wittingen, and Tom Wlodkowski.
     _________________________________________________________________
   
   [contents]   [summary]   [checklist]   [linear checklist]