From the W3C:
The User Agent Accessibility Guidelines Working Group (UAWG) has published updated Working Drafts of User Agent Accessibility Guidelines (UAAG) 2.0 and UAAG 2.0 Reference: Explanations, Examples, and Resources for User Agent Accessibility Guidelines 2.0.
UAAG 2.0 guides developers in designing user agents that make the web more accessible to people with disabilities. User agents include browsers, media players and applications that render web content.