code: def domain_xml(identifier, xml, disk_path):
      
      domain = etree.fromstring(xml)
  
      subelement(domain, './/name', 'name', identifier)
      subelement(domain, './/uuid', 'uuid', identifier)
      devices = subelement(domain, './/devices', 'devices', None)
      disk = subelement(devices, './/disk', 'disk', None, type='file', device='disk')
      subelement(disk, './/source', 'source', None, file=disk_path)
  
      return etree.tostring(domain).decode('utf-8')
docs: Fills the XML file with the required fields.
  
       * name
       * uuid
       * devices