ModelReference & Attachment base class for polymorphism

I am wanting to use polymorphism to Scan() with ModelReference & Attachment instances.  

Do these classes implement a similar interface?  

Something like IScannable?

I see that Attachment inherits from Element, but not so with ModelReference.  I was not seeing an abstract base class/interface for the shared methods.

Thanks!

I am writing in C#/C++/CLI on V8i.