_onkeyup() {
      super._onkeyup();
      this._setAffectedValue(undefined);
      if (this.startValue !== this._startValueAtBeginningOfAction || this.endValue !== this._endValueAtBeginningOfAction) {
        this.fireEvent("change");
      }
      this._startValueAtBeginningOfAction = undefined;
      this._endValueAtBeginningOfAction = undefined;
    }
Handles keyup logic. If one of the handles came across the other
swap the start and end values. Reset the affected value by the finished
user interaction.

@private