[3] CSS3 Speech Module ( ( 版)) http://www.w3.org/TR/2011/WD-css3-speech-20110419/
[1] CSS Speech Module ( ( 版)) http://www.w3.org/TR/2011/WD-css3-speech-20110818/
[2] CSS Speech Module ( ( 版)) http://www.w3.org/TR/2012/CR-css3-speech-20120320/
[6] CSS Speech Module ( ( 版)) http://dev.w3.org/csswg/css-speech/#background
[7] [css-speech] Splitting into Level 1 and Level 2 (fantasai 著, 版) https://lists.w3.org/Archives/Public/www-style/2015Jun/0347.html