docs: def _assert_is_percentage(value, maximum=100):
      """
      Makes sure the received value is a percentage. Otherwise an exception is
      thrown.
  
      :param value: the value to check
      """
  
      if value < 0 or value > maximum:
          message = 'The value on a percentage field should be between 0 and %s' \
                    % maximum
          raise pp.ParseException(message)