docs: def _format_regular_value(self, str_in):
          # type: (Text) -> Text
          """ we need to reformat integer strings, as there can be different
          strings for the same integer. The
              strategy of unification here is to first parse the integer
              string to an Integer type. Thus all of
              '+13', ' 13', '13' will be parsed to 13. We then convert the
              integer value to an unambiguous string
              (no whitespaces, leading '-' for negative numbers, no leading '+').
  
              :param str_in: integer string
              :return: integer string without whitespaces, leading '-' for
              negative numbers, no leading '+'
          """
          try:
              value = int(str_in, base=10)
              return str(value)
          except ValueError as e:
              msg = "Invalid integer. Read '{}'.".format(str_in)
              e_new = InvalidEntryError(msg)
              e_new.field_spec = self
              raise_from(e_new, e)