David Raggett; Ian Jacobs; Arnaud Le Hors. <a href="http://www.w3.org/TR/1999/REC-html401-19991224"><cite>HTML 4.01 Specification.</cite></a> 24 December 1999. W3C Recommendation. URL: <a href="http://www.w3.org/TR/1999/REC-html401-19991224">http://www.w3.org/TR/1999/REC-html401-19991224</a>