code: function _symmetricSwap(charArray, levels, params) {
        if (params.hiLevel !== 0 && _isSymmetricSwapping) {
          for (var i = 0, index; i < charArray.length; i++) {
            if (levels[i] === 1) {
              index = _SWAP_TABLE.indexOf(charArray[i]);
  
              if (index >= 0) {
                charArray[i] = _SWAP_TABLE[index + 1];
              }
            }
          }
        }
      }
docs: for reference see 7 & BD16 in http://unicode.org/reports/tr9/