code: function(terria) {
    CatalogItem.call(this, terria);
  
    /**
     * Gets or sets additional options to pass to Cesium's Cesium3DTileset constructor.
     * @type {Object}
     */
    this.options = undefined;
  
    /**
     * Gets or sets the ID of the Cesium Ion asset to access. If this property is set, the {@link Cesium3DTilesCatalogItem#url}
     * property is ignored.
     * @type {Number}
     */
    this.ionAssetId = undefined;
  
    /**
     * Gets or sets the Cesium Ion access token to use to access the tileset. If not specified, the token specified
     * using the `cesiumIonAccessToken` property in `config.json` is used. This property is ignored if
     * {@link Cesium3DTilesCatalogItem#ionAssetId} is not set.
     * @type {String}
     */
    this.ionAccessToken = undefined;
  
    /**
     * Gets or sets the Cesium Ion access token to use to access the tileset. If not specified, the default Ion
     * server, `https://api.cesium.com/`, is used. This property is ignored if
     * {@link Cesium3DTilesCatalogItem#ionAssetId} is not set.
     * @type {String}
     */
    this.ionServer = undefined;
  
    this._tileset = undefined;
  }
docs: A {@link CatalogItem} that is added to the map as Cesium 3D Tiles.
  
  @alias Cesium3DTilesCatalogItem
  @constructor
  @extends CatalogItem
  @abstract
  
  @param {Terria} terria The Terria instance.