[1] [CITE@en[CSS Image Values Module Level 3]] ([TIME[2009-07-22 06:34:16 +09:00]] 版) <http://www.w3.org/TR/2009/WD-css3-images-20090723/>

[2] [CITE@en[CSS Image Values and Replaced Content Module Level 3]]
( ([TIME[2010-12-16 06:43:56 +09:00]] 版))
<http://dev.w3.org/csswg/css3-images/>

[3] [CITE@en[CSS Image Values and Replaced Content Module Level 3]]
( ([TIME[2011-02-17 03:22:35 +09:00]] 版))
<http://www.w3.org/TR/2011/WD-css3-images-20110217/>