Chris Lilley; H&#229;kon Wium Lie. <a href="http://www.w3.org/TR/2006/WD-css3-values-20060919"><cite>CSS3 Values and Units.</cite></a> 19 September 2006. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2006/WD-css3-values-20060919">http://www.w3.org/TR/2006/WD-css3-values-20060919</a>