[1] CSS3 Generated and Replaced Content Module ( (2003-05-15 21:54:58 +09:00 版)) <http://www.w3.org/TR/2003/WD-css3-content-20030514/#line-markers>

[2] CSS Generated Content Module Level 3 ( (2011-04-21 02:28:30 +09:00 版)) <http://dev.w3.org/csswg/css3-content/#line-markers-the-line-marker-pseudo-elem>