code: def _get_xml_dom(self):
          
          if self.site_control == SITE_CONTROL_NONE and \
             any((self.domains, self.header_domains, self.identities)):
              raise TypeError(BAD_POLICY)
  
          policy_type = minidom.createDocumentType(
              qualifiedName='cross-domain-policy',
              publicId=None,
              systemId='http://www.adobe.com/xml/dtds/cross-domain-policy.dtd'
          )
          policy = minidom.createDocument(
              None,
              'cross-domain-policy',
              policy_type
          )
  
          if self.site_control is not None:
              control_element = policy.createElement('site-control')
              control_element.setAttribute(
                  'permitted-cross-domain-policies',
                  self.site_control
              )
              policy.documentElement.appendChild(control_element)
  
          for elem_type in ('domains', 'header_domains', 'identities'):
              getattr(self, '_add_{}_xml'.format(elem_type))(policy)
  
          return policy
docs: Collects all options set so far, and produce and return an
          ``xml.dom.minidom.Document`` representing the corresponding
          XML.