CustomChunks

This mod serves as an easy way for developers to customize chunks in Minecraft fabric 26.3

Set height bands in which the game believes and acts as if it was another dimension, set biome information per band or chunk and much more.

Each band is generated by the dimension it stands for, so the Nether band has real Nether terrain, mobs, light and portals, and modded or datapack dimensions work the same way as the vanilla ones.

It does nothing on its own. It is a library that other mods build on, One Dimension being the first, so you only need it when a mod asks for it.