code: function(terria) {
    ImageryLayerCatalogItem.call(this, terria);
  
    this.url = defaultValue(this.url, "//api.mapbox.com/v4/");
  
    this.mapId = undefined;
  
    this.accessToken = undefined;
  
    /**
     * Gets or sets the file extension used to retrieve Open Street Map data
     * This property is observable.
     * @type {String}
     */
    this.fileExtension = "png";
  
    /**
     * Gets or sets the maximum tile level to retrieve from Open Street Map data
     * This property is observable.
     * @type {String}
     */
    this.maximumLevel = 25;
  
    knockout.track(this, ["fileExtension", "maximumLevel"]);
  }
docs: A {@link ImageryLayerCatalogItem} representing a layer from the Mapbox server.
  
  @alias MapboxMapCatalogItem
  @constructor
  @extends ImageryLayerCatalogItem
  
  @param {Terria} terria The Terria instance.