Draft XHR spec says that responseXML must be null if parsing the response fails. But both Firefox and Safari put descriptive error documents there, with our one even being HTML.
WinIE initializes responseXML to an empty document, and keeps it empty after an error. So, the spec doesn't seem to match any major browser, but it still makes sense to me.
Created attachment 11494 [details]
I wonder if this will break any Dashboard widgets. We should test that before landing the change.
Comment on attachment 11494 [details]
Committed revision 17860 ( I assume Maciej's r+ meant that this is OK to land).