def _form_output(self):
        """ Form the output """
        self.output = u''
        if self.external_inner_xml:
            self.output += u'<Dummy_tag_to_create_valid_xml_on_external_inner'\
                           '_xml>\n'
        self.output += u'<!-- BODY -->\n{0}'.format(self.body_formatted)

        if self.external_inner_xml:
            for number, didl in enumerate(self.inner_xml):
                self.output += u'\n<!-- DIDL_{0} -->\n{1}'.\
                    format(number, etree.tostring(didl, pretty_print=True))
            self.output += u'</Dummy_tag_to_create_valid_xml_on_external_'\
                           'inner_xml>'
Form the output