
The function tries to access an XML text at location specified by document_uri
and optionally base_uri. On success, it parses the text and returns
the root entity of the "XML Tree" document; the result is identical to
the entity created by xtree_doc() PL/SQL function.

If the document_uri argument is node-set, not a string,
then a node-set is returned as if document() function is applied to string-value of every node
of the node-set.

Note that the list of attributes of the function differs from specified in XSLT 1.0 standard.
In XPATH 1.0, there is no such function at all.
