[9] HTMLEmbedElement インターフェイスの
getSVGDocument メソッドは、
次のようにしなければなりません >>7。
[17] contentDocument も参照。
普通はそちらの方が使い勝手が良さそうです。
[1] Document Structure – SVG 1.1 (Second Edition) ( ( 版)) <http://www.w3.org/TR/2011/REC-SVG11-20110816/struct.html#InterfaceGetSVGDocument>
[2] 829872 – Consider returning null from contentDocument getters when the caller does not subsume the document ( ( 版)) <https://bugzilla.mozilla.org/show_bug.cgi?id=829872>
[3] IRC logs: freenode / #whatwg / 20140806 ( ( 版)) <http://krijnhoetmer.nl/irc-logs/whatwg/20140806#l-744>
[4] Web Applications 1.0 r8713 getSVGDocument() ( ( 版)) <http://html5.org/r/8713>
[5] Web Applications 1.0 r8811 Add getSVGDocument() to object and iframe also, with the same definition as for embed. ( ( 版)) <https://html5.org/r/8811>
[6] Web Applications 1.0 r8814 getSVGDocument() can return null (IDL fix). ( ( 版)) <https://html5.org/r/8814>
[8] Merge effective script origin into origin · whatwg/html@8a843f2 ( 版) <https://github.com/whatwg/html/commit/8a843f2169a6864a3024c4329528dccb2051d275>
[19] Allow PaymentRequest and getUserMedia for same origin-domain subdocum… (zcorpan著, ) <https://github.com/whatwg/html/commit/ffae69861afaff9ca1c1f058f1d7af95412f60fa>
contentDocumentと微妙に判定条件が違っています。