code: function(item, ItemView, index){
      // get the itemViewOptions if any were specified
      var itemViewOptions = Marionette.getOption(this, "itemViewOptions");
      if (_.isFunction(itemViewOptions)){
        itemViewOptions = itemViewOptions.call(this, item, index);
      }
  
      // build the view 
      var view = this.buildItemView(item, ItemView, itemViewOptions);
      
      // set up the child view event forwarding
      this.addChildViewEventForwarding(view);
  
      // this view is about to be added
      this.triggerMethod("before:item:added", view);
  
      // Store the child view itself so we can properly
      // remove and/or close it later
      this.children.add(view);
  
      // Render it and show it
      this.renderItemView(view, index);
  
      // call the "show" method if the collection view
      // has already been shown
      if (this._isShown){
        Marionette.triggerMethod.call(view, "show");
      }
  
      // this view was added
      this.triggerMethod("after:item:added", view);
    }
docs: Render the child item's view and add it to the HTML for the collection view.