As a web developer, a number of the projects I work on fall under government umbrellas and hence are subject to 508 Accessibility laws, and sometimes W3C accessibility guidelines. To what extent can JavaScript be used while still meeting these requirements?
Along these lines, to what extent is JavaScript, specifically AJAX and using packages like jQuery to do things such as display modal dialogues, popups, etc. supported by modern accessibility software such as JAWS, Orca, etc? In the past, the rule went something like "If it won't work in Lynx, it won't work for a screen reader." Is this still true, or has there been more progress in these areas?
EDIT: The consensus seems to be that javascript is fine as long as there are non-javascript fallbacks, however it still seems uncertain about the support for AJAX in screen reader software. If anyone has specific experience with this, that would be most helpful.
If accessibility is your primary concern, always start a website using standards-compliant (pick a Document Type Definition and stick to it) HTML. If it's a web application (form submissions, etc), make sure the forms will work using just HTTP GET and POST. Once you have a complete website/application you can add bits of CSS and JavaScript as long as the site still functions, with either or both off.
The most important concept here is Progressive Enhancement. You're adding additional bells and whistles using CSS/JavaScript, but your web site/application will function perfectly well without either.
A great tool for testing 508, WAI, CSS off, JavaScript off try using the Web Developer plugin for Firefox.