[1] Extensions to CSS3 Media Queries ( ( 版)) <http://web.archive.org/web/20110903020848/http://www.webkit.org/specs/MediaQueriesExtensions.html>
[2] Chrome で試してみましたが、値は非負の <number> みたいです。
[3] Issue #9. Add -webkit-animation* to list of simple aliases. · whatwg/compat@eef5dde ( 版) <https://github.com/whatwg/compat/commit/eef5dde8fde9bff835f757b8fdf32c03427b18f8>
[4] Fixes #27. Fix -webkit-animation-direction typo. · whatwg/compat@48e278c ( 版) <https://github.com/whatwg/compat/commit/48e278c27563c08fdff2a230fb41579570c8d25a>