docs: def local_regon(self):
          """
          Returns 14 character Polish National Business Registry Number,
          local entity number.
  
          https://pl.wikipedia.org/wiki/REGON
          """
          regon_digits = [int(digit) for digit in list(self.regon())]
  
          for _ in range(4):
              regon_digits.append(self.random_digit())
  
          regon_digits.append(local_regon_checksum(regon_digits))
  
          return ''.join(str(digit) for digit in regon_digits)