This prevents the client from accidentally selected the wrong world
folder to load LODs from, since levels of the same dimension can't
naturally be distinguished from each other. With level similarity
detection, this can sometimes work, but in general is not reliable. This
mechanism instead allows servers to send a packet to the client on load,
enabling the override system, and then a second packet on world change,
which specifically sets the world key, based on knowledge that only the
server has, leading to a reliable way of detecting the correct world.
Cailin Smith
44a66a3d93