W3C Technical Architecture Group (TAG) passed down their recommendation and ended up supporting the original aria- solution present in HTML 5 and already implemented in several user-agents and JavaScript toolkits.
The TAG accepts that the most pragmatic short-term approach for WAI-PF is to go ahead and add attributes into the HTML5 spec, using names that begin “aria-” in liaison with the HTML-WG. This in no way endorses the use of the same attributes with other specs, or any XML specs, nor is this taken as being a solution for HTML versioning, HTML modularization, or HTML to XML conversions which are still open. Distributed extensibility remains an important goal for languages used on the Web, and for XML languages in particular. The TAG hopes to work with the community to strike the right balance between achieving that, and meeting the practical needs of the HTML community.
TAG had tried to push a more XML friendly namespace approach but met a lot of resistance from implementors concerned about DOM consistency.
Accessible Rich Internet Applications Suite (ARIA), defines a way to make Web content and Web applications more accessible to people with disabilities. It especially helps with dynamic content and advanced user interface controls developed with Ajax, HTML, JavaScript, and related technologies.
It is been implemented in several places including popular Javascript toolkits like DOJO and YUI. Additionally the IE8 beta ships with partial ARIA support and WebKit, one of last major UA to implement ARIA support, now has an initial implementation of the following ARIA roles: button, checkbox, heading, link, radio, textbox.
A List Apart has a crash-course for web developers interested in a higher level ARIA intro.