A slot in a component instance that can be bound to a parameter expression CompId should be a ComponentId but then we would need these types to be defined after CommonTypes. That is not possible, because we will wnat to modify CommonTypes types to use these! eventually these types can be folded into CommonTypes, and that could if need be be made recursive so solving the problem. In practice this is OK because ParamSlot is strongly typed and we will not be likely to confused CompID with any other string.