code: def _parse_doc_ref(self):
          
          command = LatexCommand(
              'setDocRef',
              {'name': 'handle', 'required': True, 'bracket': '{'})
          try:
              parsed = next(command.parse(self._tex))
          except StopIteration:
              self._logger.warning('lsstdoc has no setDocRef')
              self._handle = None
              self._series = None
              self._serial = None
              return
  
          self._handle = parsed['handle']
          try:
              self._series, self._serial = self._handle.split('-', 1)
          except ValueError:
              self._logger.warning('lsstdoc handle cannot be parsed into '
                                   'series and serial: %r', self._handle)
              self._series = None
              self._serial = None
docs: Parse the document handle.
  
          Sets the ``_series``, ``_serial``, and ``_handle`` attributes.