emit metrics about range completeness as events

A nice source of truthful delay information.
It was an attempt at Yoda-speak, not unfinished :)

Well I can move to a docstring I guess, but it is contrived (useless info for user, just my bashing of the way we do typing of events, as you can see. I can't attach a docstring to a string constant. If events were typed as classes instead of string constants, then I would have reasonable places for the useful docstrings.)