Evaluate the query, returning the result as an XdmItem (that is,
a single node or atomic value).
An XdmItem representing the result of the query, or null if the query
returns an empty sequence. If the query returns a sequence of more than one item,
any items after the first are ignored.
| Exception Type | Condition |
|---|---|
| DynamicError | Throws a DynamicError if any run-time failure occurs while evaluating the expression. |