code: function(terria) {
    this._terria = terria;
    this._eventSubscriptions = new EventHelper();
  
    /**
     * Gets the list of items that we are "now viewing".  It is recommended that you use
     * the methods on this instance instead of manipulating the list of items directly.
     * This property is observable.
     * @type {CatalogItem[]}
     */
    this.items = [];
  
    knockout.track(this, ["items"]);
  
    this.showNowViewingRequested = new CesiumEvent();
  
    this._eventSubscriptions.add(
      this.terria.beforeViewerChanged,
      function() {
        beforeViewerChanged(this);
      },
      this
    );
  
    this._eventSubscriptions.add(
      this.terria.afterViewerChanged,
      function() {
        afterViewerChanged(this);
      },
      this
    );
  }
docs: The model for the "Now Viewing" pane.