A pointer wrapper with some extra safety information about mutability.
A value representing a type which has no special UserData implementation,
It exposes the much less convenient reflect interface of the underlying type.
A reference to a rust type available from some script language.
References can be either to rust or script managed values (created either on the bevy or script side).
but also to any subfield of those values (All pointed to values must support reflect).
Each reference holds a reflection path from the root.