Right, of course, but that is an event that I would assume wouldn't require any sort of server communication or application redrawing (beyond what the native input widget already provides...)
And, if it does, it's not a situation I'm sure I would design a toolkit around...
Take an input that shows you the number of characters you typed or a form where the submit button is disabled until all required fields are filled in. These kinds of states might change on every keystroke and are not offered directly by a plain text input.