[1] なんか、 Opera 9.61 って valueAsDate 変更しても value に反映されないみたいなんですが。。。

[2] (X)HTML5 Tracking (2009-09-05 00:20:12 +09:00 版) http://html5.org/tools/web-apps-tracker?from=3749&to=3750

[3] Web Forms 2.0 (2009-01-05 20:07:15 +09:00 版) http://www.whatwg.org/specs/web-forms/current-work/#valueasdate

[4] Remove the valueAsDate branch from valueAsNumber (annevk著, 2016-07-06 15:28:28 +09:00) https://github.com/whatwg/html/commit/4ac4e10c8d5cc7fad67190365e4f823b64ad085d