If this file is present, then the mod won't load until the player goes into the Game tab of the settings window and turns it on.

This is really useful for any mods that we might want to ship with the game by default (for ease of people finding them), but make something that people have to opt into to turn on.

If ModIsDisabled.txt is present, then that overrides things to the point that the mod is invisible, and this file is ignored.