David Megginson. <a href="http://www.w3.org/TR/1999/NOTE-xml-infoset-req-19990218"><cite>XML Information Set Requirements.</cite></a> 18 February 1999. W3C Note. URL: <a href="http://www.w3.org/TR/1999/NOTE-xml-infoset-req-19990218">http://www.w3.org/TR/1999/NOTE-xml-infoset-req-19990218</a>