the actual "mechanism" is: - the server sends a HTTP response header with the requested resource like:
- if the browser caches that resource it would also maintain the Etag for that resource. - the next time that browser requests that resource it also sends a HTTP request header like:
- if the server can match Etags with the current version of that resource, instead of responding with that resource it will send a HTTP 304 Not Modified status. - then the browser will use the cached resource instead of having to wait for another copy.