Reference for “Understanding WCAG 2.0”

@TechReport{Caldwell:08:UW,
  author      = "Ben Caldwell and Gregg Vanderheiden and Loretta Guarino Reid and Michael Cooper",
  title       = "Understanding {WCAG} 2.0",
  month       = apr,
  note        = "http://www.w3.org/TR/2008/WD-UNDERSTANDING-WCAG20-20080430/",
  year        = "2008",
  bibsource   = "http://w2.syronex.com/jmr/w3c-biblio",
  type        = "{W3C} Working Draft",
  institution = "W3C",
}