As we add Ajax-powered applications for our clients and share the code with others, there is some demand to make these features available within OpenACS and .LRN. .LRN, in particular, has a goal of meeting WAI accessibility guidelines. It is very challenging to meet these guidelines with Ajax-powered systems.

At the latest OpenACS/.LRN conference, we had a discussion on new Ajax applications and accessibility. I created a wiki page to document what we learned, including links to resources and best practices, as well as draft proposals from WAI for accessible rich internet applications.

The keys are progressive enhancement  http://hesketh.com/publications/inclusive_web_design_for_the_future and unobstrusive javascript http://www.onlinetools.org/articles/unobtrusivejavascript/. These both start with a semantically correct, fully functional page without javascript. Then, javascript behaviors are added to enhance the default behavior. 

A particularly good explanation of this is Hijax progessive enahancement with ajax that says,

1. First, build an old-fashioned Web site that uses hyperlinks and forms to pass information to the server. The server returns whole new pages with each request.
2. Now, use JavaScript to intercept those links and form submissions and pass the information via XMLHttpRequest instead. You can then select which parts of the page need to be updated instead of updating the whole page.

The key is to make sure your application will work with any browser technology and, only then, add Ajax features on top of that.