[1] CSS Values and Units Module Level 3 ( ( 版)) <http://www.w3.org/TR/2015/CR-css-values-3-20150611/>
[2] Re: [css3-values][css3-speech] dB & calc() ( (Tab Atkins Jr.著, )) <https://lists.w3.org/Archives/Public/www-style/2016May/0083.html>
[3] CSS Values and Units Module Level 3 () <https://www.w3.org/TR/2016/CR-css-values-3-20160929/>
[4] [CSSWG][css-values-3] Updated CR of CSS Values and Units Level 3 (fantasai著, ) <https://lists.w3.org/Archives/Public/www-style/2018Aug/0013.html>
[5] [CSSWG][css-values-4] FPWD of CSS Values and Units Level 4 (fantasai著, ) <https://lists.w3.org/Archives/Public/www-style/2018Aug/0014.html>