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The CSS Accessibility API Mappings (CSS-AAM) defines how user agents map the Cascading Stylesheets [css-2015] features to platform accessibility APIs. It is intended for user agent developers responsible for accessibility in their user agent so that they can support the accessibility of content that uses CSS.
The CSS-AAM is part of the WAI-ARIA suite described in the WAI-ARIA Overview.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.
This is a stub document intended to collect features where CSS accessibility can be enhanced by providing user agent accessibility guidance.
This document was published by the Accessible Rich Internet Applications Working Group, the Accessible Platform Architectures Working Group, and the CSS Working Group as an Editor's Draft.
GitHub Issues are preferred for discussion of this specification. Alternatively, you can send comments to our mailing list. Please send them to public-css-a11y@w3.org (archives).
Publication as an Editor's Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by groups operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures (Accessible Rich Internet Applications Working Group), a public list of any patent disclosures (Accessible Platform Architectures Working Group), and a public list of any patent disclosures (CSS Working Group) made in connection with the deliverables of each group; these pages also include instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This document is governed by the 1 March 2019 W3C Process Document.
This section is non-normative.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, MUST NOT, OPTIONAL, RECOMMENDED, REQUIRED, SHALL, SHALL NOT, and SHOULD in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
This specification indicates whether a section is normative or informative and the classification applies to the entire section. A statement "This section is normative" or "This section is informative" applies to all sub-sections of that section.
Normative sections provide requirements that user agents must follow for an implementation to conform to this specification. The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in Keywords for use in RFCs to indicate requirement levels [RFC2119]. RFC-2119 keywords are formatted in uppercase and contained in a strong element with class="rfc2119". When the keywords shown above are used, but do not share this format,
they do not convey formal information in the RFC 2119 sense, and are merely explanatory, i.e., informative. As much as possible, such usages are avoided in this specification.
Informative sections provide information useful to understanding the specification. Such sections may contain examples of recommended practice, but it is not required to follow such recommendations in order to conform to this specification.
While some terms are defined in place, the following definitions are used throughout this document.
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 Microsoft Active Accessibility [MSAA], Microsoft User Interface Automation [UI-AUTOMATION], MSAA with UIA Express [UIA-EXPRESS], the Mac OS X Accessibility Protocol [AXAPI], the Linux/Unix Accessibility Toolkit [ATK] and Assistive Technology Service Provider Interface [AT-SPI], and IAccessible2 [IAccessible2].
An accessible object in the accessibility tree and its descendants in that tree. It does not include objects which have relationships other than parent-child in that tree. For example, it does not include objects linked via aria-flowto unless those objects are also descendants in the accessibility tree.
Tree of accessible objects that represents the structure of the user interface (UI). Each node in the accessibility tree represents an element in the UI as exposed through the accessibility API; for example, a push button, a check box, or container.
An accessible description provides additional information, related to an interface element, that complements the accessible name. The accessible description might or might not be visually perceivable.
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. See related accessible description.
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.
A node in the accessibility tree of a platform accessibility API. Accessible objects expose various states, properties, and events for use by assistive technologies. In the context of markup languages (e.g., HTML and SVG) in general, and of WAI-ARIA in particular, markup elements and their attributes are represented as accessible objects.
The action taken when an event, typically initiated by users through an input device, causes an element to fulfill a defined role. The role may be defined for that element by the host language, or by author-defined variables, or both. The role for any given element may be a generic action, or may be unique to that element. For example, the activation behavior of an HTML or SVG <a> element shall be to cause the user agent to traverse the link specified in the href attribute, with the further optional parameter of specifying the browsing context for the traversal (such as the current window or tab, a named window, or a new window); the activation behavior of an HTML <input> element with the type attribute value submit shall be to send the values of the form elements to an author-defined IRI by the author-defined HTTP method.
Hardware and/or software that:
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:
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.
A set of instance objects that share similar characteristics.
A deprecated role, state, or property is one which has been outdated by newer constructs or changed circumstances, and which may be removed in future versions of the WAI-ARIA specification. User agents are encouraged to continue to support items identified as deprecated for backward compatibility. For more information, see Deprecated Requirements in the Conformance section.
Event from/to the host operating system via the accessibility API, notifying of a change of input focus.
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.
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.
Translated to platform-specific accessibility APIs as defined in the Core Accessibility API Mappings.
A document containing graphic representations with user-navigable parts. Charts, maps, diagrams, blueprints, and dashboards are examples of graphical documents. A graphical document is composed using any combination of symbols, images, text, and graphic primitives (shapes such as circles, points, lines, paths, rectangles, etc).
Indicates that the element is not visible, perceivable, or interactive to any user. An element is considered hidden if it or any one of its ancestor elements is not rendered or is explicitly hidden.
Content provided for information purposes and not required for conformance. Content required for conformance is referred to as normative.
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 2.1 Guideline 2.1: Make all functionality available from a keyboard [WCAG21].
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 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 a result of a user interaction. 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 process them: aria-live, aria-relevant, aria-atomic, and aria-busy.
An implementing host language's primary content element, such as the body element in HTML.
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.
The Nemeth Braille Code for Mathematics is a braille code for encoding mathematical and scientific notation. See Nemeth Braille on Wikipedia.
Basic type of object in the DOM tree or accessibility tree. DOM nodes are further specified as Element or Text nodes, among other types. The nodes of an accessibility tree are accessible objects.
Required for conformance. By contrast, content identified as informative or "non-normative" is not required for conformance.
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.A description of the characteristics of classes and how they relate to each other.
Usable by users in ways they can control. References in this document relate to WCAG 2.1 Principle 2: Content must be operable [WCAG21]. See Keyboard Accessible.
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.
An 'owning element' is any DOM ancestor of the element, or any element with an aria-owns attribute which references the ID of the element.
Presentable to users in ways they can sense. References in this document relate to WCAG 2.1 Principle 1: Content must be perceivable [WCAG21].
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.
A connection between two distinct things. Relationships may be of various types to indicate which object labels another, controls another, etc.
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.
The primary element containing non-metadata content. In many languages, this is the document element but in HTML, it is the <body>.
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.
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.
Any document created from a <frame>, <iframe> or similar mechanism. A sub-document may contain a document, an application or any widget such as a calendar pulled in from another server. In the accessibility tree there are two accessible objects for this situation—one represents the <frame>/<iframe> element in the parent document, which parents a single accessible object child representing the spawned document contents.
An element specified in a WAI-ARIA relation. For example, in <div aria-controls=”elem1”>, where “elem1” is the ID for the target element.
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.
Type of DOM node that represents the textual content of an attribute or an element. A Text node has no child nodes.
Any host language attribute that would result in a user agent generating a tooltip such as in response to a mouse hover in desktop user agents.
Presentable to users in ways they can construct an appropriate meaning. References in this document relate to WCAG 2.1 Principle 3: Information and the operation of user interface must be understandable [WCAG21].
In Unicode, braille is represented in a block called Braille Patterns (U+2800..U+28FF). The block contains all 256 possible patterns of an 8-dot braille cell; this includes the complete 6-dot cell range which is represented by U+2800..U+283F. In all braille systems, the braille pattern dots-0 (U+2800) is used to represent a space or the lack of content; it is also called a blank Braille pattern. See Braille Patterns on Wikipedia.
Any software that retrieves, renders and facilitates end user interaction with Web content. This definition may differ from that used in other documents.
A reference to a target element in the same document that has a matching ID
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).
Enabling keyboard navigation in web applications is a necessary step toward making accessible web applications possible. Conforming user agents MUST conform to Supporting Keyboard Navigation requirements in [CORE-AAM].
This section MUST conform to General rules for exposing WAI-ARIA semantics in [CORE-AAM].
User agents MUST conform to Conflicts between native markup semantics and WAI-ARIA in [CORE-AAM].
User agents MUST conform to Exposing attributes that do not directly map to accessibility API properties in [CORE-AAM].
Platform accessibility APIs traditionally have had a finite set of predefined roles that are expected by assistive technologies on that platform and only one or two roles may be exposed. In contrast, WAI-ARIA allows multiple roles to be specified as an ordered set of space-separated valid role tokens. The additional roles are fallback roles similar to the concept of specifying multiple fonts in case the first choice font type is not supported.
User agents MUST conform to the Role Mapping General Rules accessibility API computational requirements in [CORE-AAM].
Translators: For label text associated with the following table and its toggle buttons, see the mappingTableLabels object in the <head> section of this document.
User agents MUST conform to the Actions accessibility API computational requirements in [CORE-AAM].
User agents fire events for user actions, WAI-ARIA state changes, changes to document content or node visibility, changes in selection, and operation of menus. Conforming user agents MUST support the [CORE-AAM] Events mappings.
User agents MUST conform to the Special Document Handling Procedures in [CORE-AAM].
This section is non-normative.
The following people contributed to the development of this document.
This publication has been funded in part with U.S. Federal funds from the Department of Education, National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR), initially under contract number ED-OSE-10-C-0067 and currently under contract number HHSP23301500054C. 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.