James Clark. <a href="http://www.w3.org/1999/06/REC-xml-stylesheet-19990629"><cite>Associating Style Sheets with XML documents.</cite></a> 29 June 1999. W3C Recommendation. URL: <a href="http://www.w3.org/1999/06/REC-xml-stylesheet-19990629">http://www.w3.org/1999/06/REC-xml-stylesheet-19990629</a>