must-revalidate

[cap97]

header("Cache-Control: public, max-age=$max_cache_age, must-revalidate");

What does the "public" and the "must-revalidate" parts mean in that header? It's part of a script that auto-thumbnails images, and the goal of that line is to cache the generated thumbnail, so they aren't constantly being reloaded every time someone hits the BACK button. It works just fine, but it also seems to work fine without the "must-revalidate" part, so I'm just curious what it's for?

[planetsim]

must-revalidate just says if you have been redo this again

[cap97]

"have been" what...? It just recreates the header over and over again? How come it still works without that statement, then?

[planetsim]

must-revalidate just says if you have been

i meant it to say if you have been previously there redo it i forgot a few words my mistake

The reason when you take it out it still works the same are a number of reasons

1) you have Cache-Control: public
2) You may not have a form. I tend to use must-revalidate when using a form incase they hit the back button