[1] CSS WG Blog – How to unprefix -webkit-device-pixel-ratio ( ( 版)) <http://www.w3.org/blog/CSS/2012/06/14/unprefix-webkit-device-pixel-ratio/>
[2] webkit, moz とも値は非負の <number> のようです。
@media (-webkit-min-device-pixel-ratio: 0) {} みたいな。[4] CSS media queries - Web developer guide | MDN ( ( 版)) <https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Media_queries#-moz-device-pixel-ratio>
[5] Issue #15. Spec -webkit-device-pixel-ratio media query feature. · whatwg/compat@0ad0180 ( 版) <https://github.com/whatwg/compat/commit/0ad018058a311e917efd6e8db3aabbb2bd468ca0>
[6] Issue #15. Let's make this a MAY. Also fix typo in name. >_> · whatwg/compat@0f1e8d0 ( 版) <https://github.com/whatwg/compat/commit/0f1e8d0513256ef6b44bd2a165799bc3318a8ade>
[7] Issue #15. Attempt to properly spec out -webkit-device-pixel-ratio. · whatwg/compat@dd9c77d ( 版) <https://github.com/whatwg/compat/commit/dd9c77d8e80a920b31db810770a1bbdd1df46dae>
[8] Fix #15: -webkit-device-pixel-radius value is <<number>> · whatwg/compat@551abca ( 版) <https://github.com/whatwg/compat/commit/551abcaaf545a8acda50b2dd31c4e1bb11b38e0f>