code: protected ListSetItem<T> newItem(IModel<T> itemModel)
  	{
  		ListSetItem<T> item = new ListSetItem<T>(Integer.toString(counter++), itemModel);
  		populateItem(item);
  		return item;
  	}
docs: Create a new ListSetItem for list item.
  
  @param itemModel object in the list that the item represents
  @return ListSetItem