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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def xml(self):
 """ Serialize this relationship collection into XML suitable for storage as a .rels file in an OPC package. """

        rels_elm = CT_Relationships.new()
        for rel in self.values():
            rels_elm.add_rel(
                rel.rId, rel.reltype, rel.target_ref, rel.is_external
            )
        return rels_elm.xml