You should read this documentation if you are a web developer who wants to store data locally on a user’s computer in amounts beyond what can reasonably be stored in an HTTP cookie.
Michael Nordman of Google asked “Is this stuff built into shipping Safari or iPhone browsers yet?”
David Kilzer replied “This feature shipped with iPhone OS 2.1. When you use “Add to Home Screen” from the “+” button on Safari for iPhone, a web application with a manifest defined (per the HTML5 spec) will be saved with any cached resources. Note that the manifest file *must* be served with the correct MIME type for this to work.
There is no shipping version of Safari for Mac OS X or Windows that supports this feature yet.”