code: def _form_output(self):
          
          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>'
docs: Form the output