If I had a user logged onto my site, having his id stored in $_SESSION, and from his browser he clicked a \'Save\' button which would make an AJAX request to th
That's what frameworks do, e.g. if you initialize session in Front Controller or boostrap script, you won't have to care about it's initalization either for page controllers or ajax controllers. PHP frameworks are not a panacea, but they do so many useful things like this!