Planeshift is a library. On its own it adds nothing you can see, no blocks, no items, no portals of its own. What it gives other mods is a way to join two dimensions with a portal plane: a surface you can look through and walk through as if the two worlds were one space.
A plane can be a finite rectangle, a doorway in a wall or infinite, joining two dimensions along an entire horizontal layer.
Register a plane; Planeshift handles the rest — drawing the far side, streaming it to the client, and carrying things across.
Planes.registerInChunks((level, chunk, out) ->
out.accept(PlaneBoundary.between(
Level.OVERWORLD, doorHere, Direction.NORTH,
Level.NETHER, doorThere, Direction.SOUTH,
Rotation.NONE).a()));
Planes can be supplied per chunk (for ones built out of blocks, which come and go), per dimension, or globally for surfaces that need no index at all.
config/planeshift.json sets how many planes may be seen through at once, how far away they stay visible, and whether entities and fluids cross them.
Under active development. Seeing through, crossing and interacting all work; expect rough edges, particularly around lighting and the seam where a fluid crosses.