Planar boundry

Description
A planar boundary is the invisible veil that separates one plane from another. Without this boundary, all of the planes would be inhabiting the same space, this would cause chaos, destruction and paradox. The boundary is a safeguard.

There are places where the boundry is thin, such as The City, this allows for a strange instance known as a planar rift.

There are also spells that can access between the planar boundary. Spells that allow users to open portals between the planes, such as planar shift which allows the caster to travel between the planes, or Banishment which allows the caster to send a planar being back to its native plane.

Planar Rifts
In places where the planar boundry is thin, it can tear, this is known as a planar rift. Where for a limited amount of time two planes inhabit the same space. The planar boundry is self repairing, and unless it is magically held open, will close very quickly. Most of the time planar rifts are very small, and very quick to fix.