#request-error part of spec:

Step 6: Fire an event named readystatechange. 

.
.

Step 9: Fire a progress event named event. // this fires the actual 'error' event

This seems to be an order of events that isn't really user-friendly. 

Given a typical XHR-using script has logic like this:

if readystatechange fires with readyState === 4
  report "success", handle response data

if error event fires
  report failure

this typical XHR user would end up running the "success" code first, then the "failure" code. This seems less than ideal.. Is there any reason we can't move the "fire error" step to before the "fire readystatechange" step?