Web Content Accessibility Guidelines 2.0

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 other words (in a name or phrase) which may be pronounced as a word

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 human language and is as up to date as the non-conformant content

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 or glyphs (typically from the 95 printable characters defined by ASCII).

Assistive technology (as used in this document )

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

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.

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

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 improve the visual readability of rendered text and images;

• screen readers, which are used by people who are blind to read textual information through synthesized speech or braille;

• text-to-speech software, which is used by some people with cognitive, language, and learning disabilities to convert text into synthetic speech;

• 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.

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

blink

turn on and off between 0.5 and 3 times per second

Note: The slower blink is in contrast with flashing, which refers to rapid changes in brightness which can cause seizures. See general flash threshold and red flash threshold.

body text

the base font used for text in a paragraph

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

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

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

Note:

context-sensitive help

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

contrast ratio

(L1 + 0.05) / (L2 + 0.05), where L1 is the relative luminance of the lighter of the foreground or background colors, and L2 is the relative luminance of the darker of the foreground or background colors.

Note 1: The relative luminance of an sRGB color is defined as 0.2126 * R + 0.7152 * G + 0.0722 * B where R, G and B are defined as:

• if R_sRGB <= 0.03928 then R = R_sRGB/12.92 else R = ((R_sRGB+0.055)/1.055) ^ 2.4

• if G_sRGB <= 0.03928 then G = G_sRGB/12.92 else G = ((G_sRGB+0.055)/1.055) ^ 2.4

• if B_sRGB <= 0.03928 then B = B_sRGB/12.92 else B = ((B_sRGB+0.055)/1.055) ^ 2.4

The "^" character is the exponentiation operator. Refer to [sRGB] and [IEC-4WD] for conversion from nonlinear to linear RGB values.

Note 2: Relative luminance values can range from 0 (black) to 1 (white), and contrast ratios can range from 1 to 21 (commonly written 1:1 to 21:1).

Note 3: For dithered colors, use average values of the colors used (average R, average G, and average B).

Note 4: Text can be evaluated with anti-aliasing turned off.

Note 5: For text displayed over gradients and background images, authors should ensure that sufficient contrast exists for each character in the content.

Note 6: A MathML version of the contrast ratio definition is available.

emergency

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

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

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 four of the following occur:

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

  2. the flashing is below 50 Hz; and

  3. the brightness of the darker image is below .80 of full scale white brightness; and

  4. the combined area of flashes occurring concurrently and contiguously occupies more than a total of .006 steradians (or one quarter of any 10 degree visual field on the screen ).

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.

Note 2: 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.

Note 3: An "opposing change" is an increase followed by a decrease, or a decrease followed by an increase.

Note 4: For general Web content, using a 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels will provide a good estimate of a 10 degree visual field of standard screen sizes and viewing distances.

human language

language that is spoken, written or signed (visually or tactilely) by humans to communicate with one another

Note: See also sign language.

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 " literally translates into "he throws a spoon," but it means that there is nothing he can do and finally he gives up.

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

Note: See also name.

legal committments

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, etc.

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].

mechanism

process or technique for achieving a result

Note 1: The mechanism may be explicitly provided in the content, or may be relied on to be provided by either the platform or by user agents, including assistive technologies.

Note 2: The mechanism must meet all success criteria for the conformance level claimed.

multimedia

audio or video synchronized with another format for presenting information and/or with time-based interactive components

multimedia alternatives to text

multimedia that presents no more information than is already presented in text (directly or via text alternatives)

Note: Multimedia alternatives to text are provided for those who benefit from alternate representations of text.

must be presented in non-text format

would be invalid if presented in text

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.

navigated sequentially

navigated in the order defined for advancing focus from one element to the next with the keyboard

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. .

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.

paused

stopped by user request and not restarted until requested by user

presentation

rendering of the content in a form to be perceived by users

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].

process

series of user actions where each action is required in order to complete an activity

Example 1: A series of Web pages on a shopping site requires users to view alternative products and prices, select products, submit an order, provide shipping information and provide payment information.

Example 2: An account registration page requires successful completion of a Turing test before the registration form can be accessed.

programmatically determined

determined by software from author-supplied data provided in a way that different user agents, including assistive technologies, can extract and present this information to users in different modalities

Example: Determined in a mark-up language from elements and attributes that are accessed directly by commonly available assistive technology.

Example: Determined from technology-specific data structures in a non-mark-up language and exposed to assistive technology via an accessibility API that is supported by commonly available assitive technology.

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.

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 supported by user agents, including assistive technologies

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) .

red flash threshold

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

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

  2. the flashing is below 50 Hz; and

  3. the combined area of flashing occurring concurrently and contiguously occupies more than a total of .006 steradians (or one quarter of any 10 degree visual field on the screen).

Note: For general Web content, using a 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 x 768 pixels will provide a good estimate of a 10 degree visual field of standard screen sizes and viewing distances.

relationships

meaningful associations between distinct pieces of content

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

same 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.

set of Web pages

collection of Web pages that have a specific relationship to each other and that are created as a body of work by an author, group or organization

Note: Different language versions would be considered different bodies of work.

Example: A set of Web pages that make up a report, a test, an exercise, a catalog, or an application.

sign language

a visual language using combinations of movements of the hands and arms, facial expressions, and body positions to convey meaning

sign language interpretation

translation of one language, generally a spoken language, into a sign language

Note: True sign languages are independent languages that are unrelated to the spoken language(s) of the same country or region.

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.

stem width

the width of the dominant stem of the font

Note: This is usually the width of the vertical stroke of the letter "T" in a Latin font (e.g. English).

structure

1. The way the parts of a Web page are organized in relation to each other; and

2. The way a collection of Web pages is organized

supplemental content

additional content that illustrates or clarifies the primary content

Example 1: 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].

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

time-dependent analog 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.

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].

used in an unusual or restricted way

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

Example: The term "gig" means something different if it occurs in a discussion of music concerts than it does in article about computer hard drive space, 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, rendering, and interacting with Web content.

user-controllable

data that is intended to be accessed by users

Note: This does not refer such things as internet logs and search engine monitoring data.

Example: Name and address fields for a user’s account.

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

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 resource that is referenced by a URI and is not embedded in another resource, plus any other resources that are used in the rendering or intended to be rendered together with it

Note: Although any "other resources" would be rendered together with the primary resource, they would not necessarily be rendered simultaneously with each other.

Example 1: A movie-like interactive shopping environment where the user visually moves about a store dragging products off of the shelves around them into a visual shopping cart in front of them. Clicking on a product causes it to be demonstrated with a specification sheet alongside.

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

Appendix B: Acknowledgments

This section is informative.

This publication has been funded in part with Federal funds from the U.S. Department of Education under contract number ED05CO0039. The content of this publication does not necessarily reflect the views or policies of the U.S. Department of Education, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

Additional information about participation in the Web Content Accessibility Guidelines Working Group (WCAG WG) can be found on the Working Group home page.

Appendix C: How to refer to WCAG 2.0 from other documents

This section is informative.

Appendix D: References

This section is informative.

I18N-CHAR-ENC

"Tutorial: Character sets & encodings in XHTML, HTML and CSS," R. Ishida, ed., This tutorial is available at http://www.w3.org/International/tutorials/tutorial-char-enc/.

IEC-4WD

IEC/4WD 61966-2-1: Colour Measurement and Management in Multimedia Systems and Equipment - Part 2.1: Default Colour Space - sRGB. May 5, 1998.

sRGB

"A Standard Default Color Space for the Internet - sRGB," M. Stokes, M. Anderson, S. Chandrasekar, R. Motta, eds., Version 1.10, November 5, 1996. A copy of this paper is available at http://www.w3.org/Graphics/Color/sRGB.html.

UAAG10

"User Agent Accessibility Guidelines 1.0," I. Jacobs, J. Gunderson, E. Hansen, eds., W3C Recommendation 17 December 2002. The latest version of UAAG 1.0 is available at http://www.w3.org/TR/UAAG10/

UNESCO

International Standard Classification of Education, 1997. A copy of the standard is available at http://www.unesco.org/education/information/nfsunesco/doc/isced_1997.htm.

UNICODE

The Unicode Consortium. The Unicode Standard, Version 4.0.1, defined by: The Unicode Standard, Version 4.0 (Reading, MA, Addison-Wesley, 2003. ISBN 0-321-18578-1), as amended by Unicode 4.0.1 (http://www.unicode.org/versions/Unicode4.0.1/).