WCAG 2.0 Conformance Proposals for 04 January 2007

Conformance

This section is normative.

Conformance means that Web content satisfies the success criteria defined in this document. This section outlines the conformance scheme used throughout this document.

WCAG 2.0 success criteria are organized into three levels of conformance. Understanding levels.

• "A" (single-A) conformance: all Level 1 success criteria must be satisfied in order to achieve A (single-A) Conformance.

• "AA" (double-A) conformance: all Level 1 and Level 2 success criteria must be satisfied in order to achieve AA (double-A) conformance.

• "AAA" (triple-A) conformance: all success criteria in Levels 1, 2, and 3 must be satisfied in order to achieve AAA (triple-A) Conformance.

The word "levels" does not mean that some success criteria are more important than others. Each success criterion in WCAG 2.0 is essential to some users, and the levels build upon each other. However, even content that conforms at AAA (triple-A) may not be fully accessible to every person with a disability.

• In general, Level 1 success criteria achieve accessibility by supporting assistive technology while putting the fewest possible limits on presentation. Thus people with a wide range of disabilities using a wide range of assistive technologies, from voice input and eye-tracking devices to screen readers and screen magnifiers, are able to access content in different ways. In other words, Level 1 success criteria support the ability of both mainstream and specialized user agents to adapt content to formats that meet their users' needs.

• The success criteria in Level 2 provide additional support for assistive technology. At the same time, they also support direct access to content by the many people who use conventional user agents without assistive technology. In general, Level 2 success criteria place more limits on visual presentation and other aspects of content than the success criteria in Level 1.

• Level 3 success criteria increase both direct access and access through assistive technology. They place tighter limits on both presentation and content.

All WCAG 2.0 success criteria are written to be testable [LC-900] . While some can be tested by computer programs, others require human testers for part or all of the test. When people who understand WCAG 2.0 and how people with different types of disabilities use the Web test the same content using the same success criteria, the same results should be obtained with a high level of confidence. [LC-1267]

For each success criterion, there is a list of techniques deemed by the Working Group to be sufficient to meet the requirement. For each sufficient technique, there is a test to determine whether the technique has been successfully implemented. If the test(s) for a "sufficient" technique (or combination of techniques) are passed, then that success criterion has been met. Passing all tests for all techniques is not necessary. It is also not necessary to meet a success criterion using one of the sufficient techniques. There may be other techniques which are not documented by the working group that would also meet the success criterion. [LC-1245]

In addition to the success criteria, which are all testable, there are a number of techniques that may enhance accessibility that are not testable or are not always appropriate. These are listed as "Advisory Techniques" in Understanding WCAG 2.0. Authors are encouraged to use these techniques where appropriate, although using them does not affect conformance.

Appendix A: Glossary

This section is normative.

abbreviation

shortened form of a word, phrase, or name

Note: Includes initialisms and acronyms.

acronym

abbreviated form made from the initial letters or parts of a name or phrase that contains several words and which may be pronounced as a word [LC-1175]

Example: NOAA is an acronym made from the initial letters of the National Oceanic and Atmospheric Administration in the United States.

activity where timing is essential

activity where timing is part of the design of the activity and removal of the time dependency would change the functionality of the content

alternate version

version that provides all of the same information and functionality in the same natural language and is as up to date as any the non-conformant content [LC-940] [LC-1490]

analog, time-dependent input

input whose result is different depending on the rate of the analog movement (such as when line width varies with pen speed or pressure)

Note: Most actions carried out by a pointing device can also be done from the keyboard (for example, clicking, selecting, moving, sizing). However, there is a small class of input that is done with a pointing device that cannot be done from the keyboard in any known fashion. This type of input can be best characterized by the fact that the outcome can only be achieved by moving the pointer in a smooth fashion at a certain rate. For example, in a watercolor program stroke width and transparency may depend on the rate of movement (and/or pressure) of a "brush." Another example would be a real-time helicopter flight simulator. [LC-1164]

Application Programming Interface (API)

definitions of how communication may take place between applications

Note 1: 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.

Note 2: A "device API" defines how communication may take place with an input or output device such as a keyboard, mouse, or video card.

Note 3: 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, the conventional input APIs of the user agent are for the mouse and keyboard. For touch screen devices or mobile devices, conventional input APIs may include stylus, buttons, and voice. The graphical display and sound card are considered conventional output devices for a graphical desktop computer environment, and each has an associated API.

Note 4: This definition is based on User Agent Accessibility Guidelines 1.0 Glossary.

ASCII art

picture created by a spatial arrangement of characters (typically from the 95 printable characters defined by ASCII).

Assistive technology (as used in this document [LC-732] )

a user agent that both:

1. provides services beyond those offered by the host user agents to meet the requirements of users with disabilities. Such services include alternative renderings (e.g., as synthesized speech or magnified content), alternative input methods (e.g., voice), additional navigation or orientation mechanisms, and content transformations (e.g., to make tables more accessible), and [LC-1178]

2. relies on services (such as retrieving Web content and parsing markup) provided by one or more other "host" user agents. Assistive technologies communicate data and messages with host user agents by using and monitoring APIs

Note 1: In this definition, the host user agents are user agents in the general sense of the term. That is, any software that retrieves and renders Web content for users. The host user agent may provide important services to assistive technologies like retrieving Web content from program objects or parsing markup into identifiable bundles. [LC-732]

Note 2: Host user agents may also provide services directly that meet the requirements of users with disabilities. [LC-732]

Note 3: This definition is based on User Agent Accessibility Guidelines 1.0 Glossary.

Example: Examples of assistive technologies that are important in the context of this document include the following:

• screen magnifiers, and other visual reading assistants, which are used by people with visual, perceptual and physical print disabilities to change text font, size, spacing, color, synchronization with speech, etc in order [LC-604] 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.

audio description

narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone

Note 1: Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content. [LC-845]

Note 2: In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)

authored component

an authored unit intended to be used as a part of another authored unit

authored unit

set of material created as a single body by an author

Example 1: a collection consisting of markup, a style sheet, and an image or audio clip.

Example 2: a set of Web pages intended to be viewed only as a unit or in sequence.

Note: This definition is based on Glossary of Terms for Device Independence.

blink

turn on and off between 0.5 and 3 times per second

captions

text presented and synchronized with multimedia to provide not only the speech, but also non-speech information conveyed through sound, including meaningful sound effects and identification of speakers [LC-846]

Note: In some countries, the term "subtitle" is used to refer to dialogue only and "captions" is used as the term for dialogue plus sounds and speaker identification. In other countries, subtitle (or its translation) is used to refer to both.

changes of context

change of :

1. user agent;

2. viewport;

3. focus;

4. content that changes the meaning of the Web page.

Note: A change of content is not always a change of context. Small changes in content, such as an expanding outline or dynamic menu, do not change the context.

conformance

satisfying all the requirements of a given standard, guideline or specification [LC-999]

content (Web content)

information and sensory experience to be communicated to the user by means of a user agent, as well as code or markup that define the structure, presentation, and interactions associated with those elements [LC-1180]

Note: This includes the code and markup that define the structure, presentation, and interaction, as well as text, images, and sounds that convey information to the end-user.

context-sensitive help

help text that provides information related to the function currently being performed

emergency

a sudden, unexpected situation or occurrence that requires immediate action to preserve health, safety, or property

event handler

section of code that responds to an action taken by the user (or user agent)

Note: On Web pages, events are usually user actions such as moving the mouse, typing, etc.

• An event handler determines the response to that action.

• A device-specific event handler only responds to an action by one kind of input device.

• An abstract event handler is one which can be activated by a variety of input devices.

extended audio description

audio description that is added to an audiovisual presentation by pausing the video so that there is time to add additional description

Note: This technique is only used when the sense of the video would be lost without the additional audio description.

full text alternative for multimedia including any interaction [LC-810]

document including correctly sequenced descriptions of all visual settings, actions, and non-speech sounds combined with descriptive transcripts of all dialogue and a means of achieving any outcomes that are achieved using interaction during the multimedia

Note: A screenplay used to create the multimedia content would meet this definition only if it was corrected to accurately represent the final multimedia after editing.

functionality

processes and outcomes achievable through user action

general flash threshold

• A sequence of flashes or rapidly changing image sequences where all three of the following occur:

  1. the combined area of flashes occurring concurrently (but not necessarily contiguously) occupies more than one quarter of any 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels;

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

  3. the flashing is below 50 Hz.

Note 1: For the general flash threshold, a flash is defined as a pair of opposing changes in brightness of 10% or more of full scale white brightness, where brightness is calculated as 0.2126 * ((R / FS) ^ 2.2) + 0.7152 * ((G / FS) ^ 2.2) + 0.0722 * ((B / FS) ^ 2.2). R, G, and B are the red, green, and blue RGB values of the color; FS is the maximum possible full scale RGB value for R, G, and B (255 for eight bit color channels); and the "^" character is the exponentiation operator. An "opposing change" is an increase followed by a decrease, or a decrease followed by an increase. This applies only when the brightness of the darker image is below .80 of full scale white brightness.

Note 2: Based on Wisconsin Computer Equivalence Algorithm for Flash Pattern Analysis (FPA)

idiom

phrase whose meaning cannot be deduced from the meaning of the individual words and the specific words cannot be changed without losing the meaning

Example 1: In English, "kicking the bucket" means "dying," but the phrase cannot be changed to "kicking the buckets" or "kicking the tub" or "booting the bucket" or "knocking over the bucket" without losing its meaning.

Example 2: In English, "spilling the beans" means "revealing a secret." However, "knocking over the beans" or "spilling the vegetables" does not mean the same thing.

Example 3: In Japanese, the phrase "さじを投げる （どうするこ ともできなくなり、あきらめること" literally translates into "he throws a spoon," but it means that there is nothing he can do and finally he gives up. [LC-1240] [LC-1382]

Example 4: In Dutch, "Hij ging met de kippen op stok" literally translates into "He went to roost with the chickens," but it means that he went to bed early.

information

1. a message to be sent and received

2. a collection of facts or data from which inferences may be drawn [LC-905]

information that is conveyed by color differences

information presented in a manner that depends entirely on the ability to perceive color

informative

for information purposes and not required for conformance

Note: Content required for conformance is referred to as "normative."

initialism

shortened form of a name or phrase made from the initial letters of words or syllables contained in that name or phrase

Note: Not defined in all languages.

Example 1: SNCF is a French initialism that contains the initial letters of the Sociétè Nationale des Chemins de Fer, the French national railroad.

Example 2: ESP is an initialism for extrasensory perception.

input error

information provided by the user that is not accepted

Note: This includes:

1. Information that is required by the Web page but omitted by the user

2. Information that is provided by the user but that falls outside the required data format or values

jargon

words used in a particular way by people in a particular field

Example: The word StickyKeys is jargon from the field of assistive technology/accessibility.

keyboard interface

interface used by software to obtain keystroke input

Note 1: Allows users to provide keystroke input to programs even if the native technology does not contain a keyboard.

Example: A touch screen PDA has a keyboard interface built into its operating system as well as a connector for external keyboards. Applications on the PDA can use the interface to obtain keyboard input either from an external keyboard or from other applications that provide simulated keyboard output, such as handwriting interpreters or speech-to-text applications with "keyboard emulation" functionality.

Note 2: Operation of the application (or parts of the application) through a keyboard-operated mouse emulator, such as MouseKeys, does not qualify as operation through a keyboard interface because operation of the program is through its pointing device interface, not through its keyboard interface.

label

text , image, or sound or other component with a text alternative that is presented to a user to identify a component within Web content

Note: See also name. [LC-847]

legal committments [LC-1471]

transactions where the person incurs a legally binding obligation or benefit

Example: A marriage license, a stock trade (financial and legal), a will, a loan, adoption, signing up for the army, a contract of any type, etcetera.

live audio-only

A time-based live presentation that contains only audio (no video and no interaction).

live video-only

A time-based live presentation that contains only video (no audio and no interaction).

lower secondary education level

the two or three year period of education that begins after completion of six years of school and ends nine years after the beginning of primary education.

Note: This definition is based on [UNESCO].

luminosity contrast ratio

(L1 + 0.05) / (L2 + 0.05), where L1 is the luminosity of the lighter of the text or background colors, and L2 is the luminosity of the darker of the text or background colors.

Note 1: The luminosity of a color is defined as 0.2126 * ((R / FS) ^ 2.2) + 0.7152 * ((G / FS) ^ 2.2) + 0.0722 * ((B / FS) ^ 2.2).

• R, G, and B are the red, green, and blue RGB values of the color.

• FS is the maximum possible full scale RGB value for R, G, and B (255 for eight bit color channels).

• The "^" character is the exponentiation operator.

Note 2: Luminosity values can range from 0 (black) to 1 (white), and luminosity contrast ratios can range from 1 to 21.

Note 3: A MathML version of the luminosity contrast ratio definition is available. [LC-603] [LC-854]

mechanism

process or technique for achieving a result

multimedia

audio or video synchronized with another type of media format for presenting information and/or with time-based interactive components [LC-1499]

must be presented in non-text format

would be invalid if presented in text [LC-1506]

Example: Color blindness test, hearing test, vision exercise, spelling test.

name

text by which software can identify a component within Web content to the user

Note: The name may be hidden and only exposed by assistive technology, whereas a label is presented even without assistive technology. In many (but not all) cases, the label is a display of the name.

natural language

languages whose rules have evolved through usage within human communities and which are used by humans to communicate with one another, including spoken, written, and signed languages languages used by humans to communicate, including spoken, written, and signed languages [LC-1184] [LC-1500]

Note: See also sign language interpretation.

non-commercial user-contributed content

content from a person/entity who is not compensated for the content that is included automatically in Web content and where the content is not edited except for censorship

non-text content

content that is not represented by a Unicode character or sequence of Unicode characters when rendered in a user agent according to the formal specification of the content type

Note: This includes ASCII Art, which is a pattern of characters and leetspeak, which is character substitution. [LC-796] .

normative

required for conformance

Note 1: One may conform in a variety of well-defined ways to this document.

Note 2: Content identified as "informative" or "non-normative" is never required for conformance.

parsed unambiguously

parsed into only one data structure

Note: Parsing transforms markup or other code into a data structure, usually a tree, which is suitable for later processing and which captures the implied hierarchy of the input.

paused

stopped by user request and not restarted until requested by user

presentation

rendering of the content and structure in a form that can be perceived by the user rendering of the content and relationships in a form that can be perceived by the user [LC-490]

primary education level

six year time period that begins between the ages of five and seven, possibly without any previous education

Note: This definition is based on [UNESCO].

programmatically determined

determined by software from data provided in a user-agent-supported manner such that the various user agents including assistive technologies can extract and present this information to users in different modalities [LC-1502]

programmatically determined link context

1. Additional information that can be programmatically determined from relationships with a link; and

2. can be extracted, combined with the link text, and presented to users in different modalities. [LC-497]

Example 1: Screen readers provide commands to read the current sentence when focus is on a link.

Example 2: Examples of information that can be extracted, combined with link text, and presented to users in different modalities include text that is in the same sentence, paragraph, list, or table cell as the link or in a table header cell that is associated with the table cell that contains the link.

programmatically set

set by software using methods that are user-agent-supported

pure decoration

serving only an aesthetic purpose, providing no information, and having no functionality.

real-time event

event that a) occurs at the same time as the viewing, b) is not completely generated by the content, and c) is not pre-recorded

Example 1: A Webcast of a live performance (occurs at the same time as the viewing and is not pre-recorded).

Example 2: An on-line auction with people bidding (occurs at the same time as the viewing).

Example 3: Live humans interacting in a fantasy world using avatars (is not completely generated by the content and occurs at the same time as the viewing) [LC-1503] .

red flash threshold

• transition to or from a saturated red where all three of the following occur:

  1. The combined area of flashes occurring concurrently occupies more than one quarter of any 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels.

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

  3. The flashing is below 50 Hz.

Note: Based on Wisconsin Computer Equivalence Algorithm for Flash Pattern Analysis (FPA)

regular expression

regular expression as defined in XML Schema Part 2: Datatypes, Appendix F. a sequence of characters that describes or matches a pattern of characters [LC-1152]

relationships

meaningful associations between distinct pieces of content [LC-1427]

role

text or a number by which software can identify the function of a component within Web content

Example: A number that indicates whether an image functions as a hyperlink, command button, or check box.

same functionality

identical result when used

Example: A submit "search" button on one Web page and a "find" button on another Web page may both have a field to enter a term and list topics in the Web site related to the term submitted. In this case, they would have the same functionality but would not be labeled consistently.

same relative order

same position relative to other items

Note: Items are considered to be in the same relative order even if other items are inserted or removed from the original order. For example, expanding navigation menus may insert an additional level of detail or a secondary navigation section may be inserted into the reading order.

sign language interpretation

translation of spoken words and other audible information into a language that uses a simultaneous combination of handshapes, facial expressions, and orientation and movement of the hands, arms, or body to convey meaning

Note: Although some languages have a signed counterpart, most sign languages are independent languages that are unrelated to the spoken language of the same country or culture.

specific sensory experience

a sensory experience that is not purely decorative and does not primarily convey important information or perform a function

Example: Examples include a performance of a flute solo, works of visual art etc. [LC-1189]

structure

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

2. The way a collection of Web pages is organized

supplemental content

additional content that users may use in addition to or instead of the default content, thatillustrates or clarifies the primary content [LC-1505]

Example 1: Examples of supplemental content may include text, images and audio. An audio version of a Web page.

Example 2: An illustration of a complex process.

Example 3: A paragraph describing the major outcomes and recommendations made in a research study.

technology

markup language, programming language, style sheet, data format, or API

text

sequence of characters

Note 1: This definition does not place requirements on the specific encoding of characters. For advice about appropriate character encodings, refer to [I18N-CHAR-ENC]. [LC-849]

Note 2: Characters are those included in the Unicode/ISO/IEC 106464 repertoire.

text alternative

programmatically determined text that is used in place of non-text content, or text that is used in addition to non-text content and referred to from the programmatically determined text

Unicode

universal character set that defines all the characters needed for writing the majority of living languages in use on computers

Note: For more information, refer to [UNICODE] or [I18N-CHAR-ENC]. [LC-849]

used in an unusual restricted way

words used in such a way that users must know exactly what definition to apply in order to understand the content correctly

Example: The word "representational" means something quite different if it occurs in a discussion of visual art as opposed to a treatise on government, but the appropriate definition can be determined from context. By contrast, the word "text" is used in a very specific way in WCAG 2.0, so a definition is supplied in the glossary.

user agent

any software that retrieves and renders Web content for users

Example: Web browsers, media players, plug-ins, and other programs — including assistive technologies — that help in retrieving and rendering Web content.

user-agent-supported

implemented by user agents including assistive technologies [LC-1509]

Note: One of the factors that should be considered before adding a technology to a baseline is the availability of affordable user agents and assistive technologies which support the technology.

variations in presentation of text

changes in the visual appearance or sound of the text; or, if auditory presentation is specified in the content, changes in the sound of text such as voice. , such as changing to a different font or a different voice [LC-852]

video

the technology of moving pictures or images

Note: Video can be made up of animated or photographic images, or both.

viewport

object in which the user agent renders content [LC-1127]

Note 1: The user agent renders content through one or more viewports. Viewports include windows, frames, loudspeakers, and virtual magnifying glasses. A viewport may contain another viewport (e.g., nested frames). User agent user interface controls such as prompts, menus, and alerts are not viewports.

Note 2: This definition is based on User Agent Accessibility Guidelines 1.0 Glossary.

Web page

a primary resource referenced by a URI and any other resources that are rendered simultaneously with it with the understanding that different sub elements or resources may be rendered simultaneously with the primary resource at different points in time.

Note: This definition is based on the definition of Web page in the Web Characterization Terminology & Definitions Sheet.

Example 1: An interactive movie-like shopping environment where the user navigates about and activates products to have them demonstrated, and moves them to a cart to buy them.

Example 2: A Web resource including all embedded images and media.

Wisconsin Computer Equivalence Algorithm for Flash Pattern Analysis (FPA)

a method developed at the University of Wisconsin, working in conjunction with Dr. Graham Harding and Cambridge Research Associates, for applying the United Kingdom's "Ofcom Guidance Note on Flashing Images and Regular Patterns in Television (Re-issued as Ofcom Notes 25 July 2005)" to content displayed on a computer screen, such as Web pages and other computer content

Note: The Ofcom Guidance Document [OFCOM] is based on the assumption that the television screen occupies the central ten degrees of vision. This is not accurate for a screen which is located in front of a person. The Wisconsin algorithm basically carries out the same analysis as the Ofcom Guidelines except that is does it on every possible ten degree window for a prototypical computer display.