Fixes #13276. Unit test is enough since the 2.x XHR transport already dismissed the XML as parsed by the XHR instance.
Removes unnecessary call to `.off()` as noted by @dcherman.
Treat an element as hidden if either offsetWidth or offsetHeight is 0. Fixes #13132, #10406.
Fix failing tests, add support for empty spans in Opera. Supplements #13132, #10406.
Ignore file inputs when serializing forms. File input serialization is handled by plugins. Fixes #13306.
Don't try and convert data for 204 No Content responses. Fixes #13292. Fixes #13261.