Bert Bos; et al. <a href="http://www.w3.org/TR/2009/CR-CSS2-20090423/"><cite>Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification.</cite></a> 23 April 2009. W3C Candidate Recommendation. (Work in progress.) URL: <a href="http://www.w3.org/TR/2009/CR-CSS2-20090423/">http://www.w3.org/TR/2009/CR-CSS2-20090423/</a>