[1] Web Controls 1.0 ( 版) <http://www.whatwg.org/specs/web-controls/current-work/#user-focus-select>
[2] Web Controls 1.0 ( ( 版)) <http://www.whatwg.org/specs/web-controls/current-work/#focus0>
[3] Web Applications Markup Language 1.0 ( ( 版)) <http://hixie.ch/specs/html/apps/web-apps-1#focus0>