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

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

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

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

[5] [CITE@en-GB-hixie[Web Controls 1.0]]
( ([TIME[2004-11-09 08:49:52 +09:00]] 版))
<http://www.whatwg.org/specs/web-controls/current-work/#focus>

[6] [CITE@en-GB-hixie[Web Applications Markup Language 1.0]]
( ([TIME[2004-04-08 02:39:12 +09:00]] 版))
<http://hixie.ch/specs/html/apps/web-apps-1#focus>

[7] [CITE@en[CSS Basic User Interface Module Level 3 (CSS3 UI)]]
( ([[Tantek Çelik]] 著, [TIME[2012-01-13 20:03:30 +09:00]] 版))
<http://www.w3.org/TR/2012/WD-css3-ui-20120117/#nav-dir>