x1=p1 is a level / world / mini-world / map / world-part / universe, of universe x2=p2=m1, with domain / sphere x3=m2 (for x1) characterized by / defined by rules x4=m3 (for x1), with parent universe of domain / sphere x5 (for x2) characterized by / defined by rules x6 (for x2)).
A mu'erpau can be nested in the x2 of another mu'erpau, forming a hierarchy.