function allowMultiple() {
                if (qq.supportedFeatures.ajaxUploading) {
                    // Workaround for bug in iOS7+ (see #1039)
                    if (self._options.workarounds.iosEmptyVideos &&
                        qq.ios() &&
                        !qq.ios6() &&
                        self._isAllowedExtension(allowedExtensions, ".mov")) {

                        return false;
                    }

                    if (spec.multiple === undefined) {
                        return self._options.multiple;
                    }

                    return spec.multiple;
                }

                return false;
            }
Generate a tracked upload button.

@param spec Object containing a required `element` property
along with optional `multiple`, `accept`, and `folders`.
@returns {qq.UploadButton}
@private