Database Software

Hi,
I need a way to declare a dynamic namespace in XmlQuery like this:

SELECT XMLQuery('declare namespace ns="$nsVar"; (::)
                 copy $i := $xml
                 modify (insert node attribute xsi:schemaLocation {"$schemaLocation"} into $i/ns:MyNode)
                 return $i'
                 PASSING xml_type AS "xml", nsVar AS "nsVar", schemaLocationVar AS "schemaLocation"
                 RETURNING CONTENT)
INTO xml_type
FROM DUAL;

Is there a way to get this to work? Because I wasn't able to.
Database Version is 19c.
Kind Regards