code: @Override
      public int mbcCaseFold(int flag, byte[]bytes, IntHolder pp, int end, byte[]lower) {
          int p = pp.value;
          int lowerP = 0;
  
          if (bytes[p] == (byte)0xdf && (flag & Config.INTERNAL_ENC_CASE_FOLD_MULTI_CHAR) != 0) {
              lower[lowerP++] = 's';
              lower[lowerP] = 's';
              pp.value++;
              return 2;
          }
  
          lower[lowerP] = LowerCaseTable[bytes[p] & 0xff];
          pp.value++;
          return 1;
      }
docs: iso_*_mbc_case_fold