[2] Selectors Level 4 ( (2011-11-15 04:03:20 +09:00 版)) <http://dev.w3.org/csswg/selectors4/#past-pseudo>
[3] Selectors Level 4 ( (2011-11-15 04:03:20 +09:00 版)) <http://dev.w3.org/csswg/selectors4/#future-pseudo>