doOne = function(options) {
            if (!$.isPlainObject(options) || !options.tileSource) {
                options = {
                    tileSource: options
                };
            }

            if (options.index !== undefined) {
                $.console.error('[Viewer.open] setting indexes here is not supported; use addTiledImage instead');
                delete options.index;
            }

            if (options.collectionImmediately === undefined) {
                options.collectionImmediately = true;
            }

            var originalSuccess = options.success;
            options.success = function(event) {
                successes++;

                // TODO: now that options has other things besides tileSource, the overlays
                // should probably be at the options level, not the tileSource level.
                if (options.tileSource.overlays) {
                    for (var i = 0; i < options.tileSource.overlays.length; i++) {
                        _this.addOverlay(options.tileSource.overlays[i]);
                    }
                }

                if (originalSuccess) {
                    originalSuccess(event);
                }

                checkCompletion();
            };

            var originalError = options.error;
            options.error = function(event) {
                failures++;

                if (!failEvent) {
                    failEvent = event;
                }

                if (originalError) {
                    originalError(event);
                }

                checkCompletion();
            };

            _this.addTiledImage(options);
        }
Raised when an error occurs loading a TileSource.

@event open-failed
@memberof OpenSeadragon.Viewer
@type {object}
@property {OpenSeadragon.Viewer} eventSource - A reference to the Viewer which raised the event.
@property {String} message - Information about what failed.
@property {String} source - The tile source that failed.
@property {?Object} userData - Arbitrary subscriber-defined object.