appcache

HTML5 mechanism http://www.w3.org/TR/2014/WD-html5-20140617/browsers.html#offline to instruct the browser to use a local cache of the page, so it works even if the website is offline.

Try serving from localhost with make, loading the file, killing the server, and then reloading the page.

HTML5 Rocks tutorial: http://www.html5rocks.com/en/tutorials/appcache/beginner/

appcache is the recommended extension for the served cache file.

Test file: test.html