[1] Refactor hasFocus() method · whatwg/html@ecce42b (2015-11-05 17:15:57 +09:00 版) <https://github.com/whatwg/html/commit/ecce42b8222a04720bfe57f0db715551b884fccf>

[2] 28090 – Request for making the steps in document.hasFocus method invokable from other spec (2016-01-26 10:47:41 +09:00 版) <https://www.w3.org/Bugs/Public/show_bug.cgi?id=28090>