Dimensions are divided into 4 types.

1. A shared dimension. A dimension which spills out into other dimensions. Various matter movement limitations might apply.
2. A fully open dimension. Matter can move in and out with no limitations.
3. A partially enclosed dimension. Matter can move in and out, however matter original to the dimension cannot leave, or original matter migration is greatly limited.
4. A fully enclosed dimension. No matter can go in or out.

Type 1 dimensions are common.