Rules:
*You can teleport into and out of it at will
*It has a couple of plug sockets and can connect to internet from the region you teleported in from
*You can take objects and people with you
*As already stated, it is 3m^3. The walls are plain plaster with a light in the middle of the ceiling. The pocket dimension is topologically toroidal, so if there weren’t walls and a ceiling/floor (which you can actually destroy) you would loop if you went more than 3m in any direction. Gravity, then, is artificial and can be altered to anywhere from 0 to 2g from a dial on the wall.
So does it just stay at the same point relative to the gravitational center of Earth? What about the day/night cycle; does the Earth keep rotating under it? And how big a mass is needed to lock it in place? It’d be pretty sweet for long plane trips if it traveled with the plane.
It stays relative to a reasonable thing, how humans would expect it to. If you were on a plane, it would stay relative to that, if you were on the ground of on the moon, similarly.