Lazy me has finally got around to sending some comments:
Under the definition of XML response entity body it is probably worth
reiterating that if the UA is not also a conforming XML UA it must
getAllResponseHeaders() should probably define the exact format. The
example makes me think that it should always output one space (U+0020)
after the colon, but currently anything is fine.
status and statusText currently MUST throw INVALID_STATE_ERR when
there isn't any status code or text respectively sent by the server.
HTTP/0.9 includes neither: Saf, Fx, and IE all return 200 and "OK",
and Op returns 0 and "". There isn't actually any issue with the
state, so throwing an INVALID_STATE_ERR makes little sense. Also, a
fair number of servers manage to omit the statusText, and that should
just return "OK" (per Saf, Fx, and IE). I'd say that it should only
throw if the state is UNSENT or OPENED.
In "Exceptions for the XMLHttpRequest Object" it would be nice to have
a note that the other exceptions are defined in DOM 3 Core.