Display form confirmation message in the same page: best practice

Question

I've seen this behaviour in many websites and web applications but I'm not able to find a "clean and standard" way to reproduce it: the user fills in the form, submits it and then, after a successful validation, the form is reloaded with a message on top saying something like "The item has been saved". No problems so far, what I can't understand is how they keep displaying the confirmation message if that specific page is reloaded, but when the user goes to another page and then returns to the original one (the one containing the form) the message is not there anymore. There seems to be no get or post data, so I'm assuming session variables or cookies are used instead, but how do they know when to keep and when to unset them? Or maybe I'm wrong and there is some other way... help me, please!

Answer 1

My guess would be that they used a session variable which unsets itself the moment that page is accessed. So if they try to access it again, they are simply redirected.

Answer 2

Maybe the page with the form doesn't have any "unset" session variable but the others do ?