Posted to site March 31, 2011

HyperText Markup Language (HTML) was not originally designed to create web applications. HTML has a limited set of interface controls, and is based around
a sequential client server communication model. Web application developers have gotten around these limitations by creating their own custom components (widgets), using JavaScript to add behaviour to the widgets.

Unfortunately, the techniques used to overcome these limitations have not been accessible. Although custom widgets might look and behave like regular desktop application widgets, such as a tree view widget, the role (what the widget does), state (its unique configuration, such as checked), and other important properties are not available to assistive technologies, such as screen readers. This is the same as styling plain text to look like a heading, rather than using a heading element — the plain text looks like a heading, but isn’t revealed as a heading to assistive technology.

Updates are often missed by people using assistive technology. Assistive technologies usually expect web content to change in response to a navigate event, such as following a link or submitting a form. Web applications use techniques, such as AJAX, to update content silently in the background, which is sometimes missed by assistive technology. Even if assistive technology is aware of updates, the user still might not be aware that the content has been updated, or how to locate the updated content.

WAI-ARIA is a specification that provides a means of describing roles, states, and properties for custom widgets so that they are recognisable and usable by assistive technology users. WAI-ARIA also provides a mechanism to ensure that users of assistive technologies are aware of updates in the application.

Read more at
http://dev.opera.com/articles/view/introduction-to-wai-aria/