All, I want to be able to spell out certain zope.schema.Object fields in my interfaces as "contained" while other fields are declared as associated/related objects. I'm interested in describing this in the interface itself, and not leave such intrinsic characteristics to the implementation class. It is useful, in my experience to have the ability for utility components to know this about a field (for example, relational database deletion cascades, JSON serialization of an object and its contained objects, neglecting related objects, or you might end up serializing the entire graph). Are there any community best practices for doing this? My previous attempts at doing this have been to subclass List and Object for OneToMany and OneToOne field types respectively, and treat original Object and List(value_type=Object()) fields as always implying containment. Is this reasonable? Are there other or better approaches? Thanks, Sean