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Appendix A Glossary (Normative)

This section is normative.


Shortened form of a word, phrase or name, i.e. a general category that includes abbreviations, initialisms and acronyms.


An abbreviation made from the initial letters of a name or phrase that contains several words. Many acronyms can be pronounced as words. Defined differently in different languages. For 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

a version that provides all of the same information and functionality and is as up to date as any non-conformant content

analog, time-dependent input

where the outcome of the input is different depending on the rate of the analog movement (such as when line width varies with pen speed or pressure.) This condition is used to make exceptions where there is no known method for allowing keyboard control but not allow exceptions for those situations were keyboard commands can be used for actions normally done with a mouse such as clicking, selecting, moving, sizing.

Application Programming Interface (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, or video card.

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: This term was taken from User Agent Accessibility Guidelines 1.0 Glossary.


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

Assistive technology

In the context of this document, an assistive technology is a user agent that:

  1. 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.

    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, and content transformations (e.g., to make tables more accessible).

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.

Note: This term was taken from User Agent Accessibility Guidelines 1.0 Glossary.

audio description

narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone. During naturally-occurring pauses in dialog, audio descriptions of video provide information about actions, characters, scene changes and on-screen text.

authored unit

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

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

background image

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


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

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


turn on and off between .5 and 3 times per second


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

changes of context

change of :

  1. user agent;

  2. viewport;

  3. focus;

  4. content that changes the meaning of the delivery unit.

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.


Information in the delivery unit that is used by the user agent to generate perceivable units. 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.

delivery unit

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

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


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

event handler

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

extended audio descriptions

audio descriptions that are added to an audio/visual presentation by pausing the video so that there is time to add addional description. This technique is only used when the sense of the video would be lost without the additional audio description.


processes and outcomes acheivable through user action

general flash threshold
  • A sequence of flashes or rapidly changing image sequences where both the following occur:

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

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

    Note: 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 .2126*R + .7152*G + .0722B using linearized R, G, and B values. Linearized-X = (X/FS)^2.2 where FS is full scale (usually 255 today). An "opposing change" is an increase followed by a decrease, or a decrease followed by an increase.

idiomatic expressions

words or phrases specific to a region or language that do not mean what the dictionary definitions of the individual words say. For example, the English phrase "he blew his stack" means that someone became very angry.

  1. A message to be sent and received,

  2. A collection of facts or data from which inferences may be drawn,

information is conveyed by color

perception of the color attributes is essential to understanding a piece of content


The shortened form of a name or phrase made from the initial letters of words or syllables contained in that name or phrase. Not defined in all languages. SNCF is a French initialism that contains the initial letters of the Societe National des Chemins de Fer, the French national railroad. ESP is an initialism for extrasensory perception.

input error

Any information provided by the user that is not accepted. This includes:

  1. information that is required by the delivery unit but omitted by the user.

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


words used in a particular way by people in a particular field. For example, the word StickyKeys is jargon from the field of assistive technology/accessibility.

keyboard interface

interface used by software to obtain keystroke input

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

A touch screen PDA has a keyboard interface built into its OS and a connector for connecting external Keyboards. Applications on the PDA can use the interface to obtain keyboard input from either 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: 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.


text that identifies a component within Web content


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

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 adapted from [UNESCO].

luminosity contrast ratio

(L1+.05) / (L2+.05) where L is luminosity and is defined as .2126*R + .7152*G + .0722B using linearized R, G, and B values. Linearized R (for example) = (R/FS)^2.2 where FS is full scale value (255 for 8 bit color channels). L1 is the higher value (of text or background) and L2 is the lower value.


a process or technique for achieving a result


audio or video synchronized with another type of media and/or with time-based interactive elements

natural languages

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

navigational mechanisms

mechanisms that allow the user to locate and/or move to a different piece of content.

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. This includes ASCII Art, which is a pattern of characters.

non-text content that conveys information

non-text content content that communicates ideas, data, facts information and is not text.

non-text content that is functional

non-text content that is capable of performing one or more actions in response to user input and is not text.

Note: This includes, but is not limited to, images used as links, image-based submit buttons, applets, and embedded programmatic objects.

non-text content that is intended to create a specific sensory experience

non-text content that causes a sensory experience that is not purely decorative and does not primarily convey important information or perform a function


Required for conformance.

parsed unambiguously

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. Parsing unambiguously means that there is only one data structure that can result

perceivable structures

relationships in the content that are necessary to perceive the organization of the content.

perceivable unit

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


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

Primary education level

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

Note: This definition is adapted from [UNESCO].

programmatically determined

can be recognized by user agents, including assistive technologies, that support the technologies in the chosen baseline

programmatic reference

functional component, such as a link or control, that causes a change of context when activated

programmatic user interface component

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

real-time events

events that are live

red flash threshold
  • A transition to or from a saturated red where both of the following occur:

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

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

regular expression

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

same functionality

Items are considered to have the same functionality if the outcome of their use is identical. For instance, a submit "search" button on one delivery unit and a "find" button on another delivery unit 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 same functionality but would not be labeled consistently.

same relative order

Each item maintains its position relative to the other items. 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 an independent language which is unrelated to the spoken language of the same country or culture.

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

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

  3. The way a collection of delivery units is organized

supplemental content

Additional content that illustrates or clarifies default text content, which users may use instead of or in addition to the default text content. For example, there may be supplements in text, graphics, and audio.


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


A sequence of characters. Characters are those included in the Unicode/ISO/IEC 106464 repertoire.

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.

unfamiliar content

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


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

Note: 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/).

URI pattern

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

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

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. For 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. This may include Web browsers, media players, plug-ins, and other programs — including assistive technologies — that help in retrieving and rendering Web content.

variations in presentations in text

Changes in the visual appearance or sound of the text, such as changing to a different font or a different voice.


the technology of moving pictures or images. Video can be made up of animated or photographic images, or both.

Wisconsin Computer Equivalence Algorithm

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