4. Important Terms

This section is informative.

While some terms are defined in place, the following definitions are used throughout this document.

Accessibility API

Operating systems and other platforms provide a set of interfaces that expose information about objects and events to assistive technologies. Assistive technologies use these interfaces to get information about and interact with those widgets. Examples of accessibility APIs are the Microsoft Active Accessibility [MSAA], the Microsoft User Interface Automation [UIA-ARIA], the Mac OS X Accessibility Protocol [AXAPI], the Linux/Unix Accessibility Toolkit [ATK] and Assistive Technology Service Provider Interface [AT-SPI], and IAccessible2 [IA2].

Accessible Name

The accessible name is the name of a user interface element. Each platform accessibility API provides the accessible name property. The value of the accessible name may be derived from a visible (e.g., the visible text on a button) or invisible (e.g., the text alternative that describes an icon) property of the user interface element.

A simple use for the accessible name property may be illustrated by an "OK" button. The text "OK" is the accessible name. When the button receives focus, assistive technologies may concatenate the platform's role description with the accessible name. For example, a screen reader may speak "push-button OK" or "OK button". The order of concatenation and specifics of the role description (e.g. "button", "push-button", "clickable button") are determined by platform accessibility APIs or assistive technologies.

Assistive Technologies

Hardware and/or software that:

relies on services provided by a user agent to retrieve and render Web content
works with a user agent or web content itself through the use of APIs, and
provides services beyond those offered by the user agent to facilitate user interaction with web content by people with disabilities

This definition may differ from that used in other documents.

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

screen magnifiers, which are used to enlarge and improve the visual readability of rendered text and images;
screen readers, which are most-often used to convey information through synthesized speech or a refreshable Braille display;
text-to-speech software, which is used to convert text into synthetic speech;
speech recognition software, which is used to allow spoken control and dictation;
alternate input technologies (including head pointers, on-screen keyboards, single switches, and sip/puff devices), which are used to simulate the keyboard;
alternate pointing devices, which are used to simulate mouse pointing and clicking.

Attribute

In this specification, attribute is used as it is in markup languages. Attributes are structural features added to elements to provide information about the states and properties of the object represented by the element.

Class

A set of instance objects that share similar characteristics.

Element

In this specification, element is used as it is in markup languages. Elements are the structural elements in markup language that contains the data profile for objects.

Event

A programmatic message used to communicate discrete changes in the state of an object to other objects in a computational system. User input to a web page is commonly mediated through abstract events that describe the interaction and can provide notice of changes to the state of a document object. In some programming languages, events are more commonly known as notifications.

Hidden

Indicates that the element is not visible or perceivable to any user. An element is only considered hidden in the DOM if it or one of its ancestor elements has the aria-hidden attribute set to true.

Note: Authors are reminded that visibility:hidden and display:none apply to all CSS media types; therefore, use of either will hide the content from assistive technologies that access the DOM through a rendering engine. However, in order to support assistive technologies that access the DOM directly, or other authoring techniques to visibly hide content (for example, opacity or off-screen positioning), authors need to ensure the aria-hidden attribute is always updated accordingly when an element is shown or hidden, unless the intent of using off-screen positioning is to make the content visible only to screen reader users and not others.

Informative

Content provided for information purposes and not required for conformance. Content required for conformance is referred to as normative.

Keyboard Accessible

Accessible to the user using a keyboard or assistive technologies that mimic keyboard input, such as a sip and puff tube. References in this document relate to WCAG 2 Guideline 2.1; "Make all functionality available from a keyboard" [WCAG20].

Landmark

A type of region on a page to which the user may want quick access. Content in such a region is different from that of other regions on the page and relevant to a specific user purpose, such as navigating, searching, perusing the primary content, etc.

Live Region

Live regions are perceivable regions of a web page that are typically updated as a result of an external event when user focus may be elsewhere. These regions are not always updated as result of a user interaction. This practice has become commonplace with the growing use of Ajax. Examples of live regions include a chat log, stock ticker, or a sport scoring section that updates periodically to reflect game statistics. Since these asynchronous areas are expected to update outside the user's area of focus, assistive technologies such as screen readers have either been unaware of their existence or unable to process them for the user. WAI-ARIA has provided a collection of properties that allow the author to identify these live regions and how to process them: aria-live, aria-relevant, aria-atomic, and aria-busy. Pre-defined live region roles are listed in the Choosing Between Special Case Live Regions ([ARIA-PRACTICES], Section 5.3).

Primary Content Element

An implementing host language's primary content element, such as the body element in HTML.

Managed State

Accessibility API state that is controlled by the user agent, such as focus and selection. These are contrasted with "unmanaged states" that are typically controlled by the author. Nevertheless, authors can override some managed states, such as aria-posinset and aria-setsize. Many managed states have corresponding CSS pseudo-classes, such as :focus, and pseudo-elements, such as ::selection, that are also updated by the user agent.

Normative

Required for conformance. By contrast, content identified as informative or "non-normative" is not required for conformance.

Object

In the context of user interfaces, an item in the perceptual user experience, represented in markup languages by one or more elements, and rendered by user agents.

In the context of programming, the instantiation of one or more classes and interfaces which define the general characteristics of similar objects. An object in an accessibility API may represent one or more DOM objects. Accessibility APIs have defined interfaces that are distinct from DOM interfaces.

Ontology

A description of the characteristics of classes and how they relate to each other.

Operable

Usable by users in ways they can control. References in this document relate to WCAG 2 Principle 2; content must be operable [WCAG20]. See Keyboard Accessible.

Owned Element

An 'owned element' is any DOM descendant of the element, any element specified as a child via aria-owns, or any DOM descendant of the owned child.

Perceivable

Presentable to users in ways they can sense. References in this document relate to WCAG 2 Principle 1; content must be perceivable [WCAG20].

Property

Attributes that are essential to the nature of a given object, or that represent a data value associated with the object. A change of a property may significantly impact the meaning or presentation of an object. Certain properties (for example, aria-multiline) are less likely to change than states, but note that the frequency of change difference is not a rule. A few properties, such as aria-activedescendant, aria-valuenow, and aria-valuetext are expected to change often. See clarification of states versus properties.

Relationship

A connection between two distinct things. Relationships may be of various types to indicate which object labels another, controls another, etc.

Role

Main indicator of type. This semantic association allows tools to present and support interaction with the object in a manner that is consistent with user expectations about other objects of that type.

Semantics

The meaning of something as understood by a human, defined in a way that computers can process a representation of an object, such as elements and attributes, and reliably represent the object in a way that various humans will achieve a mutually consistent understanding of the object.

State

A state is a dynamic property expressing characteristics of an object that may change in response to user action or automated processes. States do not affect the essential nature of the object, but represent data associated with the object or user interaction possibilities. See clarification of states versus properties.

Taxonomy

A hierarchical definition of how the characteristics of various classes relate to each other, in which classes inherit the properties of superclasses in the hierarchy. A taxonomy can comprise part of the formal definition of an ontology.

Understandable

Presentable to users in ways they can construct an appropriate meaning. References in this document relate to WCAG 2 Principle 3; Information and the operation of user interface must be understandable [WCAG20].

User Agent

Any software that retrieves, renders and facilitates end user interaction with Web content. This definition may differ from that used in other documents.

Value

A literal that solidifies the information expressed by a state, property, role, or text content.

acrWidget

Discrete user interface object with which the user can interact. Widgets range from simple objects that have one value or operation (e.g., check boxes and menu items), to complex objects that contain many managed sub-objects (e.g., trees and grids).