Of all the realities that exist within the expanse, two in particular are of concern. Neither has a proper name, as defining such a thing as a reality gets quite complicated, but are often called the abstract world and the "real" world.

The abstract world was created first, and the "real" world was created shortly after. The two realities experience an uncommon amount of overlap, like two leaves stuck together on the surface of a body of water. This is due to the nature of the creation of the "real" world, as it ballooned into existence almost on top of the abstract world.

The laws that govern the two worlds are similar, though those in the abstract world are more flexible. Put simply, the abstract world has all the same laws of governance but they can be selectively opted out of. Moreover, with enough focus, they can be ignored altogether to achieve desired outcomes. Marks of possibility are key to this, as they are both native to the abstract world and the tools by which beings that reside there overcome the laws that govern it. They, in essence, allow each resident of the world to act in the same capacity as the being that created it; though, perhaps to a lesser degree.

The "real" world has a makeup much like the world that you live in. Though, of course, it is tainted with the presence of beings from the abstract world.

Due to the overlapping, beings can cross between the two worlds. The bridges between them, however, are largely controlled by the abstract world and kept very well hidden. Only someone that knows exactly where to look and what to do, or has the guidance of an activated mark, can find them.