HTML5 accessibility implementation support in browsers

Posted on Wednesday, 18 June 2014 by Steve Faulkner

HTML5 I have been testing and tracking browser accessibility implementation support for a range of new HTML features since 2010. Data can be found on Over the last week I also undertook a more formal, targeted testing of the normative implementation requirements in the WAI-ARIA section of the HTML5.0 specification which is currently on its way to becoming a W3C Recommendation.

Understanding the testing results

HTML5 contains normative requirements (things a browser MUST implement) to be considered to support HTML5. In order for HTML5.0 to become a W3C Recommendation the normative requirements must be implemented interoperably (i.e. in at least 2 independent browsers). One of the methods used to decide whether a given HTML feature is implemented interoperably is to create tests and test the assertions in the specification in browsers. Details of the requirements are in the Model CR Exit Criteria (Public Permissive version 3).

In the case of accessibility semantics implementation the assertions are framed in terms of ARIA roles, states and properties as implicit ARIA semantics. For example:

HTML feature Implicit ARIA semantics
button element button role

Another step is required

ARIA semantics in this case are used as an abstract indicator of the platform specific requirements. To find out and test what browsers are actually required to implement to conform to the above requirement we have to refer to the ARIA implementation guide, which describes the implementation requirements for ARIA semantics in terms of the platform accessibility API mappings

MSAA + UIA Express role (IE on windows) MSAA + IAccessible2 role andother IAccessible2 features (Firefox chrome on windows) ATK/AT-SPI role (firefox on linux) Mac OS XAXRole
(Safari, Chrome, Firefox on OSX)

So from this information it can be assessed whether a browser passes or fails the assertion that the button element has a button role by looking at what role the browser exposes via the platform accessibility API(s) it has implemented (noted browser/platform in table headers) . We can look at the accessibility information (roles and properties) by using an object inspection tool, such as aViewer inspect.exe or a11y-probe.

For example, using aViewer it can be confirmed that Firefox 29 on Windows exposes the correct role for the button element:

button element information exposed in MSAA and Iaccessible2 by Firefox 29 is role of button.

The results of testing all the assertions within the WAI-ARIA section of the HTML5.0 Last Call Working Draft specification are available: Implementation status for HTML5 element/attribute accessibility mappings


The accessibility requirements specified in the HTML5.0/5.1 specifications are only a subset of browser accessibility implementation requirements. Much of what is needed is simply not specified in any HTML specification. Work is continuing on a HTML accessibility mapping and related specifications to fully define the requirements on browsers to support HTML and SVG accessibility.

The testing conducted is for the purposes of checking HTML5 Last Call Working Draft specification support, these are a subset of the requirements contained in the (still in development) HTML 5.1 specification,  features that do not have at least 2  implementations  are absent from HTML5.0 (e.g. dialog element).

About Steve Faulkner

Steve is the Technical Director at TPG. He joined The Paciello Group in 2006 and was previously a Senior Web Accessibility Consultant at vision australia. He is the creator and lead developer of the Web Accessibility Toolbar accessibility testing tool. Steve is a member of several groups, including the W3C Web Platforms Working Group and the W3C ARIA Working Group. He is an editor of several specifications at the W3C including HTML 5.1, ARIA in HTML, Notes on Using ARIA in HTML and HTML5: Techniques for providing useful text alternatives. He also develops and maintains HTML5accessibility.


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