[1] CSS3 module: Basic User Interface ( (Tantek Çelik 著, 2002-08-03 07:13:43 +09:00 版)) <http://www.w3.org/TR/2002/WD-css3-ui-20020802/#nav-dir>

[2] CSS3 Basic User Interface Module ( (Tantek Çelik 著, 2003-07-04 02:51:33 +09:00 版)) <http://www.w3.org/TR/2003/WD-css3-ui-20030703/#nav-dir>

[3] CSS3 Basic User Interface Module ( (Tantek Çelik 著, 2004-05-12 02:17:47 +09:00 版)) <http://www.w3.org/TR/2004/CR-css3-ui-20040511/#nav-dir>

[4] CSS Basic User Interface Module Level 3 (CSS3 UI) ( (Tantek Çelik 著, 2011-09-29 17:32:08 +09:00 版)) <http://dev.w3.org/csswg/css3-ui/#nav-dir>