XMLType.isFragment — The function returns 1 if the instance is
an XML generic entity or 0 if it is a plain document.
The function checks the number of children elements of the root
of the document root of the given instance. If there are no such
documents or there are many of them then the document is not
well-formed, for example it can not be fully validated against an
XML schema. However it can be used as a fragment of a larger
document: it can be declared as an external generic entity and then
referenced in a top-level document or in one of its subdocuments.
For example a book can be stored in XML as a root document that
includes subdocuments, one or more chapter per subdocument.
The function returns 1 if the given XMLType instance is a
fragment and returns 0 if it is a well-formed XML document.
Integer value 1 or 0.
The table DB.DBA.SYS_USERS always contains more than one user
record so the call of XMLAGG that returns one element per record
creates an valid generic entity but not a valid document.