Reference for “XML Path Language (XPath) 2.1”

@TechReport{Dyck:09:XPL,
  author      = "Michael Dyck and Jonathan Robie and John Snelson and Don Chamberlin",
  title       = "{XML} Path Language ({XPath}) {2.1}",
  month       = dec,
  note        = "http://www.w3.org/TR/2009/WD-xpath-21-20091215/",
  year        = "2009",
  bibsource   = "http://w2.syronex.com/jmr/w3c-biblio",
  type        = "{W3C} Working Draft",
  institution = "W3C",
}