Reads: "A <draw:object> shall use only one method of containment for any instance of that element."

<draw:object> only contains objects, first issue.

Is this a general restriction on the same object not appearing from different sources that are contained by <draw:object>?

But that would read (possibly): "An object shall only appear in one OpenDocument representation for any one <draw:object> element."

Which indirectly means you only get one containment. Yes?