ScreenWaitResult.dropped_bytes

One accepted screen wait. text is the screen of the matching read, cut to a tail of at most max_bytes bytes, and dropped_bytes counts the bytes cut from its head. When max_bytes cuts the screen, the match can lie in the dropped head, so text need not contain it. matched_at_entry is true exactly when the match was on the entry read, and then source == :baseline; otherwise source == :output.