XForms CR - 3.3.2 "one and the same"?

In 3.3.2 the sentence, "We also seek feedback on self-referential cases where 
the instance data and the containing document are one and the same." is used 
to refer to an open issue.

Since, to the best of my knowledge, instance data can (more or less) only 
exist when an <xforms:instance> element is nested within an <xforms:model> 
element I don't see how the "instance data" and the "containing document" can 
ever be "one and the same".

Quite possibly I am missing some significant point but some clarification 
would be helpful.

Andrew Watt