[1] [CITE[IRC logs: freenode / #whatwg / 20120713]]
( ([TIME[2012-07-21 01:41:48 +09:00]] 版))
<http://krijnhoetmer.nl/irc-logs/whatwg/20120713#l-817>

[2] [CITE@en[CSS Values and Units Module Level 3]]
([TIME[2015-12-08 20:47:23 +09:00]] 版)
<https://drafts.csswg.org/css-values-3/#about-invalid>