CSS Accessibility API Mappings

W3C Editor's Draft

This version:
http://w3c.github.io/css-aam/
Latest published version:
https://www.w3.org/TR/css-aam-1.0/
Latest editor's draft:
http://w3c.github.io/css-aam/
Editor:
To Be Determined

Abstract

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.

Status of This Document

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.

Comments regarding this document are welcome. 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.

1. Introduction

This section is non-normative.

2. Conformance

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 are to be interpreted as described in [RFC2119].

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.

3. Important Terms

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 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].

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.
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.

Informative

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

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.
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.

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.

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.

Widget

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).

4. Supporting Keyboard Navigation

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].

5. Mapping WAI-ARIA to Accessibility APIs

5.1 General rules for exposing WAI-ARIA semantics

This section MUST conform to General rules for exposing WAI-ARIA semantics in [CORE-AAM].

6. Conflicts between native markup semantics and WAI-ARIA

User agents MUST conform to Conflicts between native markup semantics and WAI-ARIA in [CORE-AAM].

7. Exposing attributes that do not directly map to accessibility API properties

User agents MUST conform to Exposing attributes that do not directly map to accessibility API properties in [CORE-AAM].

8. Role mapping

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.

8.1 General Rules

User agents MUST conform to the Role Mapping General Rules accessibility API computational requirements in [CORE-AAM].

8.2 Feature Mapping Table

Editor's note

Translators: For label text associated with the following table and its toggle buttons, see the mappingTableLabels object in the <head> section of this document.

9. Special Processing Requiring Additional Computation

9.1 Generated Content

10. Actions

User agents MUST conform to the Actions accessibility API computational requirements in [CORE-AAM].

11. Events

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.

12. Special Document Handling Procedures

User agents MUST conform to the Special Document Handling Procedures in [CORE-AAM].

A. Appendices

A.1 Change Log

A.2 Acknowledgments

This section is non-normative.

The following people contributed to the development of this document.

A.2.1 Participants of the APA, ARIA, and CSS Working Groups who contributed to this document

TBD

A.2.2 Enabling funders

This publication has been funded in part with Federal funds from the U.S. Department of Education, National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR) under contract number ED-OSE-10-C-0067. 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.

B. References

B.1 Normative references

[AT-SPI]
Assistive Technology Service Provider Interface. The GNOME Project. URL: https://developer.gnome.org/libatspi/stable/
[ATK]
ATK - Accessibility Toolkit. The GNOME Project. URL: https://developer.gnome.org/atk/stable/
[AXAPI]
The NSAccessibility Protocol for macOS. Apple, Inc. URL: https://developer.apple.com/documentation/appkit/nsaccessibility
[CORE-AAM-1.1]
Core Accessibility API Mappings 1.1. Joanmarie Diggs; Joseph Scheuhammer; Richard Schwerdtfeger; Michael Cooper; Andi Snow-Weaver; Aaron Leventhal. W3C. 14 December 2017. W3C Recommendation. URL: https://www.w3.org/TR/core-aam-1.1/
[css-2015]
CSS Snapshot 2015. Tab Atkins Jr.; Elika Etemad; Florian Rivoal. W3C. 13 October 2015. W3C Note. URL: https://www.w3.org/TR/css-2015/
[IAccessible2]
IAccessible2. Linux Foundation. URL: https://www.linuxfoundation.org/collaborate/workgroups/accessibility/iaccessible2
[MSAA]
Microsoft Active Accessibility (MSAA) 2.0. Microsoft Corporation. URL: https://msdn.microsoft.com/en-us/library/ms697707.aspx
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[UI-AUTOMATION]
UI Automation. Microsoft Corporation. URL: https://msdn.microsoft.com/en-us/library/ee684009%28v=vs.85%29.aspx
[UIA-EXPRESS]
The IAccessibleEx Interface. Microsoft Corporation. URL: https://msdn.microsoft.com/en-us/library/windows/desktop/dd561898%28v=vs.85%29.aspx
[WCAG21]
Web Content Accessibility Guidelines (WCAG) 2.1. Andrew Kirkpatrick; Joshue O Connor; Alastair Campbell; Michael Cooper. W3C. 5 June 2018. W3C Recommendation. URL: https://www.w3.org/TR/WCAG21/