docs: function handleEvent(mapBrowserEvent) {
    let stopEvent = false;
    if (mapBrowserEvent.type == EventType.KEYDOWN ||
        mapBrowserEvent.type == EventType.KEYPRESS) {
      const keyEvent = /** @type {KeyboardEvent} */ (mapBrowserEvent.originalEvent);
      const charCode = keyEvent.charCode;
      if (this.condition_(mapBrowserEvent) &&
          (charCode == '+'.charCodeAt(0) || charCode == '-'.charCodeAt(0))) {
        const map = mapBrowserEvent.map;
        const delta = (charCode == '+'.charCodeAt(0)) ? this.delta_ : -this.delta_;
        const view = map.getView();
        zoomByDelta(view, delta, undefined, this.duration_);
        mapBrowserEvent.preventDefault();
        stopEvent = true;
      }
    }
    return !stopEvent;
  }