code: function( opacity ) {
          $.console.error("drawer.setOpacity is deprecated. Use tiledImage.setOpacity instead.");
          var world = this.viewer.world;
          for (var i = 0; i < world.getItemCount(); i++) {
              world.getItemAt( i ).setOpacity( opacity );
          }
          return this;
      }
docs: Set the opacity of the drawer.
  @param {Number} opacity
  @return {OpenSeadragon.Drawer} Chainable.