An offline web application revolves around a cache manifest file. What’s a manifest file? It’s a list of all of the resources that your web application might need to access while it’s disconnected from the network. In order to bootstrap the process of downloading and caching these resources, you need to point to the manifest file, using a manifest attribute on your element.
Your cache manifest file can be located anywhere on your web server, but it must be served with the content type text/cache-manifest.