[1] [whatwg] Outline style to use for drawSystemFocusRing ( (2013-07-27 06:52:19 +09:00 版)) <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2013-July/040255.html>

[2] [whatwg] Outline style to use for drawSystemFocusRing ( (2013-09-10 23:35:02 +09:00 版)) <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2013-September/040764.html>

[3] [whatwg] Outline style to use for drawSystemFocusRing ( (2013-10-16 20:36:49 +09:00 版)) <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2013-October/041134.html>

[4] IRC logs: freenode / #whatwg / 20140122 ( (2014-01-24 19:49:50 +09:00 版)) <http://krijnhoetmer.nl/irc-logs/whatwg/20140122>

[5] [whatwg] Outline style to use for drawSystemFocusRing ( (2014-01-25 09:33:27 +09:00 版)) <http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2014-January/041930.html>

[6] Web Applications 1.0 r8854 Drop drawCustomFocusRing(), since no browsers have indicated interest in implementing it, and rename drawSystemFocusRing() to drawFocusIfNeeded() to match implementations. (2014-11-20 09:14:00 +09:00 版) <https://html5.org/r/8854>