All play moves and has its being within a play-ground marked off beforehand either materially or ideally, deliberatly or as a matter of course. The arena, the card-table, the magic circle, the temple, etc., are all in form and function play-grounds, i.e., forbidden spots, isolated, hedged round, hallowed, within which special rules obtain. All are temporary worlds within the ordinary world, dedicated to the performance of an act apart.