Evaluate the expression, returning the result as an IEnumerator
(that is,
an enumerator over a sequence of nodes and/or atomic values).
An enumerator over the sequence that represents the results of the expression.
Each object in this sequence will be an instance of XdmItem
. Note
that the expression may be evaluated lazily, which means that a successful response
from this method does not imply that the expression has executed successfully: failures
may be reported later while retrieving items from the iterator.