[1] [CITE@en[Compound Document by Reference Framework 1.0]]
( ([TIME[2010-08-17 16:50:04 +09:00]] 版))
<http://www.w3.org/TR/CDR/#child-to-parent-dom-access>

[2] [CITE@en-US[Window Object 1.0]]
( ([TIME[2006-04-08 02:19:28 +09:00]] 版))
<http://www.w3.org/TR/Window/#embedding>

[3] [CITE@en[829872 – Consider returning null from contentDocument getters when the caller does not subsume the document]]
( ([TIME[2013-11-13 20:44:00 +09:00]] 版))
<https://bugzilla.mozilla.org/show_bug.cgi?id=829872>

[4] [CITE@en[868235 – window.frameElement should throw for cross-origin parents]]
( ([TIME[2013-11-13 21:24:15 +09:00]] 版))
<https://bugzilla.mozilla.org/show_bug.cgi?id=868235>