code: private boolean checkPlVatId(final String pvatId) {
      final int checkSum = pvatId.charAt(11) - '0';
      final int sum = (pvatId.charAt(2) - '0') * 6 + (pvatId.charAt(3) - '0') * 5
          + (pvatId.charAt(4) - '0') * 7 + (pvatId.charAt(5) - '0') * 2 + (pvatId.charAt(6) - '0') * 3
          + (pvatId.charAt(7) - '0') * 4 + (pvatId.charAt(8) - '0') * 5 + (pvatId.charAt(9) - '0') * 6
          + (pvatId.charAt(10) - '0') * 7;
      final int calculatedCheckSumPl = sum % MODULO_11;
      return checkSum == calculatedCheckSumPl;
    }
docs: check the VAT identification number, country version for Poland.
  
  @param pvatId vat id to check
  @return true if checksum is ok