This interface abstracts handling of property sets for elements with children.
Imagine elements such as mixers or polyphonic generators. They all have multiple Pad or some kind of voice objects. Another use case are container elements like Bin. The element implementing the interface acts as a parent for those child objects.
Property names are written as "child-name::property-name". The whole naming scheme is recursive. Thus "child1::child2::property" is valid too, if "child1" and "child2" implement the ChildProxy interface.