ambiguity in XQuery grammar

There appears to be an ambiguity in the current draft specification's grammar, which I was hoping someone could resolve for me.

Consider:

1 instance of xs:integer+ +1

Is this equivalent to:

(1 instance of xs:integer+) +1

or:

(1 instance of xs:integer) + (+1)

?

I would suggest changing the syntax for InstanceOfExpr so parentheses are put around the SequenceType.