When assertions are evaluated, a data model instance must be constructed for
the evaluation.  The Structures spec needs to explain how that data model
instance is created and in particular make clear what type labels it has.

The WG has discussed this at length in the context of a more general proposal
for 'tree trimming', and agreed at the meeting of Friday 23 March to adopt
the 'Moses' proposal, which involves validating as much of the element in
question as is feasible without checking its assertions, building a PSVI to 
reflect that partial validation, and using the resulting data model instance.
There is one point of concern about this procedure:  when the element in 
question has a complex type with simple content, it seems unfortunate that the
value of the element itself is not typed.  So the editors were asked to see
if a simple way could be found to type the value.  (This addition to the
Moses proposal has acquired the soubriquet "Moses supposes".)

The data model construction rules should also be applicable to XPath
evaluation in identity constraints and in conditional type assignment,
should the WG adopt a conditional-type proposal.