this is a feature which is very important for event based programming its basically added to an event to make it perform its action only once e.g. you make an event which says, shoot object A out of object B when Object B's animation is on frame 2, sounds fine, but theres a problem, object b will shoot as many objects as it can during that frame, so if its anim speed is lets say, 25, object b will shoot 3 shots b4 the frame changes, if you were to make the event {shoot object A out of object B when Object B's animation is on frame 2 and add to that only one action when event loops} then your object b would shoot only 1 bullet when its on frame 2 regardless of how long it stays on that frame, which is the desired action.
plz implement in next build
and if its already there some1 plz tell me where it is