[1] Web Forms 2.0 (1/5/2009, 11:07:15 AM 版) <http://www.whatwg.org/specs/web-forms/current-work/#valueasnumber>

[2] Remove the valueAsDate branch from valueAsNumber (annevk著, 7/6/2016, 6:28:28 AM) <https://github.com/whatwg/html/commit/4ac4e10c8d5cc7fad67190365e4f823b64ad085d>