WAI = Web Accessibility Initiative
ARIA = Accessible Rich Internet Applications
It's a W3C Specification, like HTML, CSS, XML etc.
It is very close to becoming a W3C Recommendation.
It makes sense
The addition of a role attribute
<a href="" title="OK" role="button"> <img src="ok.gif" alt="OK"> </a>
Correct role information: "Button"
Usage instructions: "To activate press spacebar"
<input type="image" src="ok.gif" alt="OK">
Wherever possible use native HTML elements.
button not selected
<input type="image" src="hioff.gif" alt="highlight">
<input type="image" src="hion.gif" alt="highlight">
button not selected
<input type="image" src="hioff.gif" alt="highlight" role="button" aria-pressed="false">
<input type="image" src="hion.gif" alt="highlight" role="button" aria-pressed="true">
Two main issues:
Live Regions solves the 2nd issue. The first issue and why it occurs is detailed in AJAX and Screen Readers - Content Access Issues
Users who rely on their sight as the primary sense are able to access web content in a non-linear fashion. So they can percieve much more content at any given moment.
Users who access web content aurally do so linearly and have much more limited access to content at a given moment.
Solves the second problem:
"Users not being aware of content changes."
In the case of the twitter character countdown, visual users can easily monitor the character count as it changes.
Live regions provides a similar capability to aural users: The value of the character count is announced at their convenience, without the need to move focus away from writing a message in the text box.
Using Live Regions provides access to content updates.
"ARIA is the most important technology to help people with disabilities since the ability for application components to expose their accessibility information"
Support is also being implemented in JQuery
HTML 4 + WAI-ARIA = HTML more
ARIA provides additional accessibility features to those natively available in HTML 4
HTML5 + WAI-ARIA = HTML more
HTML5 will provide some extra inbuilt support for accessibility, but this support is not expected to be as extensive as that provided by WAI-ARIA. Furthermore it is envisaged that some of the accessibility features currently available in HTML 4 may not be implemented in HTML5, WAI-ARIA features could fill in the gaps.