* 歴史

[1] [CITE@en[Selectors]]
( ([TIME[2001-01-16 00:22:58 +09:00]] 版))
<http://www.w3.org/TR/1998/WD-css2-19980128/selector.html#h-5.7.1.1>


[2] [CITE@en[Fix #991: Define case-sensitivity of the argument to attr() · whatwg/html@fb8ed61]]
([TIME[2016-04-14 11:49:25 +09:00]] 版)
<https://github.com/whatwg/html/commit/fb8ed61b69109b14dc8ffac5dbca6d04aab28ca8>

[3] [CITE@en[''''''[''''''css-values'''''']'''''' Generify the handling of units in the attr() type arg. · w3c/csswg-drafts@1741f95]]
([TIME[2016-04-28 14:51:24 +09:00]] 版)
<https://github.com/w3c/csswg-drafts/commit/1741f95fc91ef2309daa5a1000a4d7b0197c652a>

[4] [CITE@en[435426 - implement css3-values extensions to attr()]]
([TIME[2017-10-15 18:16:34 +09:00]])
<https://bugzilla.mozilla.org/show_bug.cgi?id=435426>

[5] [CITE@en[246571 - Implement CSS3 attribute / attr references - chromium - Monorail]]
([TIME[2017-10-15 18:17:28 +09:00]])
<https://bugs.chromium.org/p/chromium/issues/detail?id=246571>

[6] [CITE@en[Use CSS Syntax tokens for attr()]]
([[csnardi]]著, [TIME[2018-02-09 06:37:19 +09:00]])
<https://github.com/w3c/csswg-drafts/commit/d65e80d0dcec8b8943a4844b24cad42c79d53de2>

[7] [CITE@en[Use CSS Syntax tokens for attr() by csnardi · Pull Request #2293 · w3c/csswg-drafts]]
([TIME[2018-02-11 17:30:33 +09:00]])
<https://github.com/w3c/csswg-drafts/pull/2293>