It appears that when jqXHR.readyState (i.e., the readyState field of the first parameter to the $.ajax(...).fail() method) is 0 that a network error has occurred. However, I have not been able to ascertain what the exact network error is via JavaScript.
I have looked at the jQuery Ajax code, and xhr.send() (i.e., the XMLHttpRequest.send()) method (which generates the network error) does not catch nor throw the error. Thus, it is not possible to catch it.
It appears that the browser detects and displays the correct error message but that jQuery is oblivious to the specific type of network error that occurs.
