Glossary

Accessible Name

The accessible name is the programmatically determined name of a user interface element that is included in the accessibility tree.

The accessible name is calculated using the accessible name and description computation.

For native markup languages, such as HTML and SVG, additional information on how to calculate the accessible name can be found in HTML Accessibility API Mappings 1.0, Accessible Name and Description Computation (working draft) and SVG Accessibility API Mappings, Name and Description (working draft).

For more details, see examples of accessible name.

Note: As per the accessible name and description computation, each element always has an accessible name. When no accessible name is provided, the element will nonetheless be assigned an empty ("") one.

Note: As per the accessible name and description computation, accessible names are flat string trimmed of leading and trailing whitespace. Notably, it is not possible for a non-empty accessible name to be composed only of whitespace since these must be trimmed.

Accessibility Support for Accessible Name

  • Because the accessible name and description computation is not clear about which whitespace are considered, browsers behave differently when trimming and flattening the accessible name. For example, some browsers completely trim non-breaking spaces while some keep them in the accessible name.
  • There exists a popular browser which does not perform the same trimming and flattening depending whether the accessible name comes from content, an aria-label attribute, or an alt attribute.
  • There exists a popular browser which assign no accessible name (null) when none is provided, instead of assigned an empty accessible name ("").
  • The accessible name and description computation suggest that if an aria-labelledby attribute refers to an existing but empty element, the computation should stop and return an empty name without defaulting to the next steps. Several user agents and assistive technologies chose to use the next step in the computation in this case.

Attribute value

The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.

Some notable case of attribute value, among others:

  • For enumerated attributes, the attribute value is either the state of the attribute, or the keyword that maps to it; even for the default states. Thus <input type="image" /> has an attribute value of either Image Button (the state) or image (the keyword mapping to it), both formulations having the same meaning; similarly, "an input element with a type attribute value of Text" can be either <input type="text" />, <input /> (missing value default), or <input type="invalid" /> (invalid value default).
  • For boolean attributes, the attribute value is true when the attribute is present and false otherwise. Thus <button disabled>, <button disabled="disabled"> and <button disabled=""> all have a disabled attribute value of true.
  • For attributes whose value is used in a case-insensitive context, the attribute value is the lowercase version of the value written in the HTML code.
  • For attributes that accept numbers, the attribute value is the result of parsing the value written in the HTML code according to the rules for parsing this kind of number.
  • For attributes that accept sets of tokens, whether space separated or comma separated, the attribute value is the set of tokens obtained after parsing the set and, depending on the case, converting its items to lowercase (if the set is used in a case-insensitive context).
  • For aria-* attributes, the attribute value is computed as indicated in the WAI-ARIA specification.

This list is not exhaustive, and only serves as an illustration for some of the most common cases.

The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.

Changes in content

A event originated change in the content of a web page occurs when, by comparing the web page before and 1 minute after the event firing, at least one of the following occurs:

  • visible changes: the rendered pixels change in any part of the document that is currently within the viewport or that can be brought into the viewport via scrolling; or
  • accessibility tree changes: any state, property or event of a node representing an accessible object of the accessibility tree changes, or any node is inserted in, or removed from the accessibility tree; or
  • audible changes: the audio rendered by the web page changes.
  • If the web page is rendering time-based media, rendered pixels and audio will be changing as part of the playback. The comparison in this instance should compare the pixels and audio that are rendered if the event is not fired, with the ones that are rendered if the event is fired.

Assumptions:

  • This definition assumes that there are no changes in the content of the web page caused by another event. If this is not the case, changes may be attributed to the wrong event.
  • This definition assumes that the changes happen within a 1 minute time span after the event firing and therefore the comparison between the page before and after the event firing can be made at any time after that time span elapses. If there are changes after this time span, this definition may not detect them. The arbitrary 1 minute time span, selected so that testing this rule would not be impractical, is not included in WCAG.

Clearly labeled location

Secondary information and alternative controls of functionality are often not displayed together with primary information or functionality. For example, an option to change a web page to dark mode may be placed on an options page instead of being available on every page and page state of a website. Another example is a maps application, where, instead of using GPS, an option is available in a dropdown menu to set the current location of the device. Such content should be placed in a clearly labeled location.

The location of a target is said to be clearly labeled when the target can be found by activating "identifiable" instruments which either lead the user to find the target, or to another page or page state from which this action can be repeated until the target is found.

Whether or not the content is "clearly labeled" depends on the starting point of the search. If page A has a link which clearly "identifies" some piece of content, then the location of the content is clearly labeled. Page B, which can be in the same website, may not have such a link or may have a link with a link text that does not "identify" target content or which can be interpreted to "identify" more than one target, and so the location of the content starting from page B is not clearly labeled.

For the purpose of this definition, an instrument is identifiable if any text or other content with a text alternative, allows any user to identify an element with a semantic role that inherits from widget.

A web page changes state when the document's body changes without a change in the document's URL.

Clipped by Overflow

A node with an ancestor in the flat tree with a computed overflow of none or clipped, where changing the overflow of all such ancestors to visible would cause more of the node to become visible.

Example of clipped by overflow for Clipped by Overflow

This img element has an ancestor div element with an overflow of none (both overflow-x and overflow-y). The height of the img is greater than that of the ancestor div, and so is clipped by the overflow property of the div.

<div style="height: 100px; overflow: none;">
	<img src="/test-assets/w3c-logo.png" height="150" alt="Partial W3C Logo" />
</div>

Default Page Language

The default page language is the most common language used in a web page. If there are no words in the page, the default language is undefined.

The most common language is determined by counting the number of words in the web page that are part of any of the languages in the language subtag registry. The same word can be part of multiple languages. If the number of words is the same, the default language is undefined.

The words used in the following texts should be counted for the most common language:

Exception: Do not count words in text that comes from nodes that have an ancestor in the flat tree which has a non-empty ("") lang attribute and is not the root node. For accessible texts, only ancestors of the node with the accessible name is considered, the ancestry of nodes used in producing the accessible text are ignored, such as those referenced with aria-labelledby.

Disabled Element

An element is considered disabled when it has been rendered inoperable using one of the following properties:

  1. The disabled attribute. The presence of this attribute, regardless of its value, on a

    will disable the element itself if it is not a fieldset or, if it is, will disable any descendants of the element, excluding those that are descendants of the first legend child of the element.

    Note: When the disabled attribute is specified on a fieldset element, shadow-including descendants are not disabled by default. Such behavior may however be explicitly implemented by form-associated custom elements.

  2. The aria-disabled attribute. The presence of this attribute with a value that is an ASCII case-insensitive match for true on an element will communicate its state, and the state of its shadow-including descendants, as "disabled" to assistive technology.

    Note: When the aria-disabled attribute is specified on an element, it is assumed that the element has also been disabled for users that do not rely on assistive technology. For example, this can be done by disabling pointer events using the pointer-events property and by disabling keyboard interactions using the tabindex attribute.

Used In Rules: (1)

Equivalent resource

Non-identical resources can still be equivalent resources by equally complying to the expectation formed by the user when navigating to them, thus serving an equivalent purpose. This would usually involve that the advertised key content is the same.

Web pages and documents (e.g. PDFs, office formats etc.) may be equivalent resources, even if the resources:

  • are located on different URLs, including different domains
  • present different navigation options, e.g. through bread crumbs or local sub menus
  • contain different amounts of information and/or differently worded information
  • use different layouts.

If all resources cover the user's expectations equally well, the resources are considered to be equivalent.

Note: The user's expectations for the resource can be formed by different things, e.g. the name of the link leading to the resource, with or without the context around the link. This depends on the accessibility requirement that is tested.

Note: If the same content is presented in different formats or languages, the format or language itself is often part of the purpose of the content, e.g. an article as both HTML and PDF, an image in different sizes, or an article in two different languages. If getting the same content in different formats or languages is the purpose of having separate links, the resources are not equivalent.

Explicit Semantic Role

The explicit semantic role of an element is determined by its role attribute (if any).

The role attribute takes a list of tokens. The explicit semantic role is the first valid role in this list. The valid roles are all non-abstract roles from WAI-ARIA Specifications. If the element has no role attribute, or if it has one with no valid role, then this element has no explicit semantic role.

Other roles may be added as they become available. Not all roles will be supported in all assistive technologies. Testers are encouraged to adjust which roles are allowed according to the accessibility support base line. For the purposes of executing test cases in all rules, it should be assumed that all roles are supported by assistive technologies so that none of the roles fail due to lack of accessibility support.

Accessibility Support for Explicit Semantic Role

Some browsers and assistive technologies treat the tokens of the role attribute as case-sensitive. Unless lowercase letters are used for the value of the role attribute, not all user agents will be able to interpret the tokens correctly. ARIA in HTML (working draft) also specifies that authors must use lowercase letters for the role and aria-* attributes.

Filename

A filename is a text string that identifies an electronically stored file. In a URL it is located at the end of the path, after the last slash and before any query strings. For example the src attribute specifies a URL path of src="/foo/bar.jpg?baz " which contains the filename bar.jpg.

Focusable

Elements that can become the target of keyboard input as described in the HTML specification of focusable and can be focused.

Used In Rules: (43)

Foreground Colors Of Text

The colors of all the pixels of a visible character in a text node that change color when the CSS color property is changed. This includes anti-aliased pixels.

Note: Anti-aliasing is a technique in which the foreground color and background color are blended to create smooth edges.

Used In Rules: (1)

Form Field Error Indicator

Any text, or non-text content, or an element that has presentation indicating that an error was identified which appears to be related to some user input into, or the lack of user input into some element. These could be different types of errors, for example:

  • missing input, for example a required form field that was left empty
  • incorrect input, such as an invalid password
  • input not in an expected format, expected range, or of an allowed value
  • timing error, such as session timeouts or expiration of an allowed action
  • authentication or authorization errors

Note: An error indicator can be a separate element in the page, but it can also be part of a form control. For example a red outline on a form control is often used to indicate an error. Not all red outlines are indicators of an error though. This depends on the presentation of the form control in relation to other elements on the page.

Hidden State

An HTML element's hidden state is "true" if at least one of the following is true for itself or any of its ancestors in the flat tree:

  • has a hidden attribute; or
  • has a computed CSS property display of none; or
  • has a computed CSS property visibility of hidden; or
  • has an aria-hidden attribute set to true

In any other case, the element's hidden state is "false".

Implicit Semantic Role

The implicit semantic role of an element is a pre-defined value given by the host language which depends on the element and its ancestors.

Implicit roles for HTML and SVG, are documented in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

Accessibility Support for Implicit Semantic Role

  • Images with an empty alt attribute should have an implicit role of presentation, according to the HTML Accessibility API Mapping (work in progress). However, there are several popular browsers that do not treat images with empty alt attribute as having a role of presentation. Instead, they add the img element to the accessibility tree with a role of either img or graphic.

Included in the accessibility tree

Elements included in the accessibility tree of platform specific accessibility APIs. Elements in the accessibility tree are exposed to assistive technologies, allowing users to interact with the elements in a way that meet the requirements of the individual user.

The general rules for when elements are included in the accessibility tree are defined in the core accessibility API mappings. For native markup languages, such as HTML and SVG, additional rules for when elements are included in the accessibility tree can be found in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

For more details, see examples of included in the accessibility tree.

Note: Users of assistive technologies might still be able to interact with elements that are not included in the accessibility tree. An example of this is a focusable element with an aria-hidden attribute with a value of true. Such an element could still be interacted using sequential keyboard navigation regardless of the assistive technologies used, even though the element would not be included in the accessibility tree.

Used In Rules: (41)

Instrument to achieve an objective

An HTML element that when activated allows an end-user to achieve an objective.

Note: Any rule that uses this definition must provide an unambiguous description of the objective the instrument is used to achieve.

Marked as decorative

An element is marked as decorative if one of the following conditions is true:

  • it has an explicit role of none or presentation; or
  • it is an img element with an alt attribute whose value is the empty string (alt=""), and with no explicit role.

Elements are marked as decorative as a way to convey the intention of the author that they are pure decoration. It is different from the element actually being pure decoration as authors may make mistakes. It is different from the element being effectively ignored by assistive technologies as rules such as presentational roles conflict resolution may overwrite this intention.

Elements can also be ignored by assistive technologies if their hidden state is true. This is different from marking the element as decorative and does not convey the same intention. Notably, the hidden state of an element may change as users interact with the page (showing and hiding elements) while being marked as decorative should stay the same through all states of the page.

Matching characters

A sequence of characters is considered to match another if, after removing leading and trailing space characters and replacing remaining occurrences of one or more space characters with a single space, the two sequences of characters are equal character-by-character, ignoring any differences in letter casing.

Non-streaming media element

A non-streaming media element is an HTML Media Element for which the duration property is not 0.

Outcome

An outcome is a conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target. An outcome can be one of the three following types:

  • Inapplicable: No part of the test subject matches the applicability
  • Passed: A test target meets all expectations
  • Failed: A test target does not meet all expectations

Note: A rule has one passed or failed outcome for every test target. When there are no test targets the rule has one inapplicable outcome. This means that each test subject will have one or more outcomes.

Note: Implementations using the EARL10-Schema can express the outcome with the outcome property. In addition to passed, failed and inapplicable, EARL 1.0 also defined an incomplete outcome. While this cannot be the outcome of an ACT Rule when applied in its entirety, it often happens that rules are only partially evaluated. For example, when applicability was automated, but the expectations have to be evaluated manually. Such "interim" results can be expressed with the incomplete outcome.

Owned by

An element A is owned by element B if element A is a child of element B in the accessibility tree.

Being a child in the accessibility tree is different from being a child in the DOM tree. Some DOM nodes have no corresponding node in the accessibility tree (for example, because they are marked with role="presentation"). A child in the accessibility tree can thus correspond to a descendant in the DOM tree. Additionally, the use of aria-owns attribute can change the tree structure to something which is not a subtree of the DOM tree.

This definition is different from the definition of "owned element" in WAI-ARIA. Because browsers have different accessibility trees, which element owns which other elements can vary between browsers. Until there is a standard accessibility tree, testing with multiple accessibility trees may be necessary.

Programmatically Determined Link Context

The programmatically determined context of a link (or programmatically determined link context) is the set of all elements that are included in the accessibility tree, and have one of the following relationships to the link:

This definition is based on the WCAG definition of programmatically determined link context.

This definition assumes that the HTML document with the link is a document using HTML according to the specification.

Rendered text

An element is considered to have rendered text when it contains text nodes that do not inherit from an element that is styled with display:none or visibility:hidden. The rendered text is a string of the concatenated data of all these text nodes.

Used In Rules: (0)

No Data

Same resource

Two or more resources can be the same resource even though the URLs for them are different. This can be due to URL parsing, server settings, redirects and DNS aliasing.

If the parsed URLs for two resources are identical, the resources are the same resource.

Depending on the server, URLs can either be case-sensitive or case-insensitive, meaning that <a href="page1.html"> and <a href="Page1.html"> lead to either the same or two different pages.

Fully parsed URLs can be different, but still lead to the same resource after making the HTTP request, due to redirects and DNS aliasing. For example, these URLs are all fully normalized: http://example.com/, http://www.example.com/, https://www.example.com/. The server can however be configured to serve the same site for http and https, and the same site for example.com and www.example.com. This is common, but not guaranteed.

Some types of redirects are also caused by user agents, e.g. ensuring that http://example.com/ and http://example.com resolve to the same resource.

On the other hand, identical relative URLs do not necessarily resolve to the same resource, even if they are in the same web page (HTML). This happen because external content can be included through iframe and URLs in or out of it will resolve relatively to different base URLs.

Scrollable Elements

A scrollable element is an element with a horizontal scroll distance or a vertical scroll distance greater than 0.

note: Elements such as iframe which can render a nested browsing context are not scrollable elements. The scrollbars on some iframe elements come from the content inside the nested browsing context.

Semantic Role

The semantic role of an element is determined by the first of these cases that applies:

  1. Conflict If the element is marked as decorative, but the element is included in the accessibility tree; or would be included in the accessibility tree when its hidden state is false, then its semantic role is its implicit role.
  2. Explicit If the element has an explicit role, then its semantic role is its explicit role.
  3. Implicit The semantic role of the element is its implicit role.

Accessibility Support for Definition of Semantic Role for Semantic Role

  • There exist popular web browsers and assistive technologies which do not correctly implement Presentational Roles Conflict Resolution. These technologies will not include in the accessibility tree elements that should be, according to Specifications. Thus, some elements that should have their semantic role fixed by case Conflict above are instead falling into case Explicit and are hidden for users of assistive technologies.
  • A similar conflict exists for focusable elements with a aria-hidden="true" attribute. The WAI ARIA specification does not explain how to solve it. Some browsers give precedence to the element being focusable (and expose it in the accessibility tree) while some give precedence to the aria-hidden attribute (and hide the element).

Standard keyboard navigation

Standard keyboard navigation entails using one or more of the following:

  • Tab key
  • Shift+Tab
  • Arrow keys
  • Esc key
  • Enter key
  • Space key

Expected behavior of standard keyboard navigation keys:

  • Tab key: Skipping forward between focusable elements
  • Shift+Tab: Skipping backwards between focusable elements
  • Arrow keys: Navigate input elements, e.g. up/down drop down, between radio buttons etc.
  • Esc key: Close or cancel, e.g close a modal
  • Enter key: Select or activate the element in focus (same as clicking with mouse)
  • Space key: Select input elements, e.g. drop downs, radio buttons etc.

Valid Language Tag

A language tag is valid if its primary language subtag exists in the language subtag registry with a Type field whose field-body value is language.

A "language tag" is here to be understood as in the first paragraph of the BCP 47 language tag syntax, i.e. a sequence of subtags separated by hyphens, where a subtag is any sequence of alphanumerical characters. Thus, this definition intentionally differs from the strict BCP 47 syntax (and ABNF grammar) as user agents and assistive technologies are more lenient in what they accept. The definition is however consistent with the behavior of the :lang() pseudo-selector as defined by Selectors Level 3. For example, de-hello would be an accepted way to indicate German in current user agents and assistive technologies, despite not being valid according to BCP 47 grammar. As a consequence of this definition, however, grandfathered tags are not correctly recognized as valid language subtags.

Subtags, notably the primary language subtag, are case insensitive. Hence comparison with the language subtag registry must be done in a case insensitive way.

Visible

Content perceivable through sight.

Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.

Content is defined in WCAG.

For more details, see examples of visible.

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Visual Context

The visual context of a node is everything that is visually or logically located near it when the document containing it is rendered. Only visible information may be part of the visual context.

The logical distance is the distance in the structure of the document: either the tree distance within the DOM tree, or the semantic relation. For example, headings are logically near the content that follows (until the next heading of the same or higher level) even though they might be far away visually or in the DOM tree.

The visual context may include, but is not limited to, headings, text in the same sentence or paragraph.

Note: As a rule of thumb, visual context should be close enough to be displayed on the device at the same time as the element it relates to. Because device sizes vary wildly and content can further be zoomed and moved around, this is however not a strong requirement.

Note: Visual context that is located before (in reading order) the element it relates to is often more useful than visual context located after. Indeed, it is easier for users to use context that they have already read than context that is yet to be read.

WAI-ARIA specifications

The WAI ARIA Specifications group both the WAI ARIA W3C Recommendation and ARIA modules, namely:

Note: depending on the type of content being evaluated, part of the specifications might be irrelevant and should be ignored.

Web page (HTML)

An HTML web page is the set of all fully active documents which share the same top-level browsing context.

Note: Nesting of browsing context mostly happens with iframe and object. Thus a web page will most of the time be a "top-level" document and all its iframe and object (recursively).

Note: Web pages as defined by WCAG are not restricted to the HTML technology but can also include, e.g., PDF or DOCX documents.

Note: Although web pages as defined here are sets of documents (and do not contain other kind of nodes), one can abusively write that any node is "in a web page" if it is a shadow-including descendant of a document that is part of that web page.

Whitespace

Whitespace are characters that have the Unicode "White_Space" property in the Unicode properties list.

This includes:

  • all characters in the Unicode Separator categories, and
  • the following characters in the Other, Control category:

    • Character tabulation (U+0009)
    • Line Feed (LF) (U+000A)
    • Line Tabulation (U+000B)
    • Form Feed (FF) (U+000C)
    • Carriage Return (CR) (U+000D)
    • Next Line (NEL) (U+0085)

viewport size

The viewport size is the width and height at which a page is rendered. The viewport size is equal to the innerWidth and innerHeight of the window of the top-level browsing context.

Note: The viewport size is not to be confused with the "resolution" of the operating system. Often a browser will be a single window in the operating system, with a width and height different from the resolution of the operating system. Often browsers also include additional user interface components, such as a URL bar, tab bar, and a bookmarks bar. None of these are included in the viewport size. In full screen mode the viewport size might be the same as the resolution of the operating system.

Note: The viewport size includes, if rendered, all scrollbars.