Iterator that returns all the external references of the markable
        @rtype: L{CexternalReference}
        @return: the external references

def get_external_references(self):
        """
        Iterator that returns all the external references of the markable
        @rtype: L{CexternalReference}
        @return: the external references
        """
        for ext_ref_node in self.node.findall('externalReferences'):
            ext_refs_obj = CexternalReferences(ext_ref_node)
            for ref in ext_refs_obj:
                yield ref