In a two part series on his site Suresh Ariya shows you how to implement "flash messages" in your applications (in a framework-agnostic way) with the help of a custom script and the current user's session.

As part of the post series, today we are going to see how we can implement Flash Messages using PHP Session. Before proceeding into that, first i like to explain what is Flash Message and its usage. [...] Flash message is a message that will be shown/displayed only once. if you reload the browser or navigated to other pages and came back, you won't see the same message displayed again.

In part one he introduces the concepts behind flash messaging and gets into the initial steps of the implementation via a "FlashMessageInterface" to define the structure. In part two he gets into the actual implementation and shares a script that uses a custom prefix to define the messages and the expected getter/setter methods as well as "clear" functionality.