function _getKeyString(weEvt){
        var sMainKey = htVar.htKeycodeMap[weEvt.keyCode];
        if(typeof sMainKey === "undefined"){ // ignore event if not on keyMap
            return;
        }

        // generate key combination
        var aKeys = [];
        var sKeyString = "";

        if(weEvt.altKey){
            aKeys.push("ALT");
        }

        if(weEvt.ctrlKey || weEvt.metaKey){
            aKeys.push("CTRL");
        }

        if(weEvt.shiftKey){
            aKeys.push("SHIFT");
        }

        aKeys.push(sMainKey);
        sKeyString = aKeys.join("+").toUpperCase();

        return sKeyString;
    }
generate key string from keyDown event
@param {Wrapped Event} weEvt