code: function() {
          $.console.error("drawer.getOpacity is deprecated. Use tiledImage.getOpacity instead.");
          var world = this.viewer.world;
          var maxOpacity = 0;
          for (var i = 0; i < world.getItemCount(); i++) {
              var opacity = world.getItemAt( i ).getOpacity();
              if ( opacity > maxOpacity ) {
                  maxOpacity = opacity;
              }
          }
          return maxOpacity;
      }
docs: Get the opacity of the drawer.
  @returns {Number}