I can think of lots of options too...
multi value property (I know)
composite property
virtual page
internal page
internal object (I know)
Ultimately, I think "subobject" and "has subobject" win in my head
because of precedence. I don't think 'object' is too far from the
truth here, in so far as
Here is another aggregated reply, this time about the naming.
I agree that #subobject is not ideal. I agree that "object" has
technical connotations, but not that they are necessarily related to
anything specific; it's just a very general term that has all kinds of
meanings in all kinds of area
