http://www.html5rocks.com/en/tutorials/file/filesystem/#toc-file-appending

http://stackoverflow.com/questions/13752984/html5-file-api-downloading-file-from-server-and-saving-it-in-sandbox

http://my.safaribooksonline.com/book/web-development/html/9781449311384

I tested the following Javascript code in Xcode 5.0 and iPhone Simulator 7.0 with iOS 7:

if('requestFileSystem' in window) {
alert("requestFileSystem in window:" + (typeof window.requestFileSystem));
}

The result shows that window.requestFileSystem() exists but its type is "undefined".
Its type should be 'function' to be called.
I guess its name is reserved but not implemented yet.