[1] DOM 4 request ( (Richard Schwerdtfeger 著, 版)) http://lists.w3.org/Archives/Public/www-dom/2013JanMar/0171.html
[2] [whatwg] Document.activeElement should return the root element in non-HTML documents when no element has focus ( ( 版)) http://lists.whatwg.org/pipermail/whatwg-whatwg.org/2014-February/041974.html
[3] Editorial: synchronize with the DOM Standard · whatwg/html@21c6ec7 ( 版) https://github.com/whatwg/html/commit/21c6ec77594eb89b836d4872222f5916910967fd
[4] Editorial: cleanup activeElement (annevk著, ) https://github.com/whatwg/html/commit/4823cf596e2ce499f3be67b486ffea261cbe4b29
[5] Editorial: cleanup activeElement by annevk · Pull Request #3513 · whatwg/html () https://github.com/whatwg/html/pull/3513
[6] Define DocumentOrShadowRoot's activeElement (rakina著, ) https://github.com/whatwg/html/commit/5b84d194c5ca0be9b738e0d46078131ca4a5f422
[7] Define DocumentOrShadowRoot.activeElement by rakina · Pull Request #4837 · whatwg/html () https://github.com/whatwg/html/pull/4837
[8] Shadow DOM and focus · Issue #1583 · whatwg/html () https://github.com/whatwg/html/issues/1583