code: function( item, options ) {
          $.console.assert(item, "[World.addItem] item is required");
          $.console.assert(item instanceof $.TiledImage, "[World.addItem] only TiledImages supported at this time");
  
          options = options || {};
          if (options.index !== undefined) {
              var index = Math.max(0, Math.min(this._items.length, options.index));
              this._items.splice(index, 0, item);
          } else {
              this._items.push( item );
          }
  
          if (this._autoRefigureSizes) {
              this._figureSizes();
          } else {
              this._needsSizesFigured = true;
          }
  
          this._needsDraw = true;
  
          item.addHandler('bounds-change', this._delegatedFigureSizes);
          item.addHandler('clip-change', this._delegatedFigureSizes);
  
          /**
           * Raised when an item is added to the World.
           * @event add-item
           * @memberOf OpenSeadragon.World
           * @type {object}
           * @property {OpenSeadragon.Viewer} eventSource - A reference to the World which raised the event.
           * @property {OpenSeadragon.TiledImage} item - The item that has been added.
           * @property {?Object} userData - Arbitrary subscriber-defined object.
           */
          this.raiseEvent( 'add-item', {
              item: item
          } );
      }
docs: Add the specified item.
  @param {OpenSeadragon.TiledImage} item - The item to add.
  @param {Number} [options.index] - Index for the item. If not specified, goes at the top.
  @fires OpenSeadragon.World.event:add-item
  @fires OpenSeadragon.World.event:metrics-change