None of these should be required on a web site:
The Web Content Accessibility Guidelines, v.2, are based on four guiding principles:
Experience and Observation
Good advice is:
Bad advice is likely to be absolutist or reductionist.
HTML code is written in a specific order, and the screen reader must follow that.
WAVE is a product from WebAIM, out of Utah State University and the Center for People with Disabilities
WCAG Recommended Techniques: highly technical, though simpler than the WCAG itself. http://www.w3.org/TR/WCAG-TECHS/
WebAIM: Simplified summaries, recommendations. Extensive documentation on almost every accessibility topic: http://webaim.org
University of Minnesota, Duluth Web Design References: Extensive curated catalog of accessibility articles on the web: http://bit.ly/t3tPZC