code: def _WriteHeader(self, output_writer):
      
      header_string = ''
      if self._title:
        header_string = ' {0:s} '.format(self._title)
  
      header_string = self._HEADER_FORMAT_STRING.format(header_string)
      output_writer.Write(header_string)
docs: Writes a header.
  
      Args:
        output_writer (OutputWriter): output writer.