Ian Hickson; H&#229;kon Wium Lie. <a href="http://www.w3.org/TR/2003/WD-css3-preslev-20030813"><cite>CSS3 module: Presentation Levels.</cite></a> 13 August 2003. W3C Working Draft. (Work in progress.) URL: <a href="http://www.w3.org/TR/2003/WD-css3-preslev-20030813">http://www.w3.org/TR/2003/WD-css3-preslev-20030813</a>