xmlsequence has two forms:
- The first form takes as input an XMLType instance and returns
a varray of the top-level nodes in the XMLType.
- The second form takes as input a REFCURSOR instance, with an
optional instance of the XMLFormat object, and returns as an
XMLSequence type an XML document for each row of the cursor.
Because xmlsequence returns a collection of XMLType, you
can use this function in a TABLE clause to unnest the collection values
into multiple rows, which can in turn be further processed in the SQL
query.