Also, to demonstrate the importance of this:
For exemple this.inst.GetWorldInfo()._SetLayer()
The reason _SetLayer() is marked private (via the underscore) and is undocumented, is because it is an internal engine call. It must be used simultaneously with a range of other calls across the engine, otherwise it will corrupt the internal state of the runtime and break the game. In other words, it's not useful on its own, and using it will break things. This is true of any other features you find that are undocumented.
This has been a huge pain for us and other people before. Please do not go and write code using stuff like this.