function _normalizeKeyString(sKey){
        sKey = sKey.toUpperCase() || "";
        sKey = sKey.replace(htVar.rxTrim, '');
        sKey = sKey.split("+").sort(function(v){
            return -1 * (htVar.aCombinationKeys.indexOf(v));
        }).join("+");

        return sKey;
    }
normalize Key String
@param {String} sKey