File: file/js/file.js

                /**
                 * The File class provides a wrapper for a file pointer, either through an HTML5
                 * implementation or as a reference to a file pointer stored in Flash. The File wrapper
                 * also implements the mechanics for uploading a file and tracking its progress.
                 * @module file
                 * @main file
                 * @since 3.5.0
                 */
            
                /**
                 * `Y.File` serves as an alias for either <a href="FileFlash.html">`Y.FileFlash`</a>
                 * or <a href="FileHTML5.html">`Y.FileHTML5`</a>, depending on the feature set available
                 * in a specific browser.
                 *
                 * @class File
                 */
            
             var Win = Y.config.win;
            
             if (Win && Win.File && Win.FormData && Win.XMLHttpRequest) {
                Y.File = Y.FileHTML5;
             }
            
             else {
                Y.File = Y.FileFlash;
             }