tab(event) {
        var _this$responder28;
        if ((_this$responder28 = this.responder) !== null && _this$responder28 !== void 0 && _this$responder28.canDecreaseNestingLevel()) {
          var _this$responder29;
          (_this$responder29 = this.responder) === null || _this$responder29 === void 0 || _this$responder29.decreaseNestingLevel();