WAI: Strategies, guidelines, resources to make the Web accessible to people with disabilities

Accessibility Information for Specific Technologies

XML Accessibility Guidelines Working Draft: Draft document.
Accessibility Features of CSS: (old document)
Accessibility Features of SMIL: (old document)
Accessibility Features of SVG: (old document)
HTML 4.0 Accessibility Improvements: (old document)

See also:

Web Content Accessibility Guidelines (WCAG) Overview - Includes links to techniques associated with WCAG, including CSS Techniques.