This is basically a reference to a C++ `ServerActiveObject`.

### Advice on handling `ObjectRefs`

When you receive an `ObjectRef` as a callback argument or from another API

function, it is possible to store the reference somewhere and keep it around.

It will keep functioning until the object is unloaded or removed.

However, doing this is **NOT** recommended as there is (intentionally) no method

to test if a previously acquired `ObjectRef` is still valid.

Instead, `ObjectRefs` should be "let go" of as soon as control is returned from

Lua back to the engine.

Doing so is much less error-prone and you will never need to wonder if the

object you are working with still exists.