Passing information between frames

I tried posting this to the news group yesterday, but it didn't show up. Anyway, I have two frames and need to pass information between them. Frame A holds a.php, a presentation of items which the user can select (enter the number, hit the "buy" button). Frame B holds b.php, a list of selected items (shopping basket). a.php uses POST to tell b.php what the user just selected. b.php then appends the last selection to its list. (The information from the B frame is later posted to an order system.) What I would like is for the A frame to see this list aswell, so that I could pass the whole list and the new item to b.php in the B frame, let b.php concatenate the old list and the new item into the new list, and then let a.php in the A frame become aware of the new list as well. Then the whole thing could happen again the next time the "buy" button is pressed. I guess I could update the entire frameset, there encoding the list in A's URL. But bandwidth may be pretty low and I don't want the user to scroll back to where he/she was in the A frame before hitting the "buy" button. The reason for wanting this is that I won't need cookies or server-side storage of the shopping basket. Any tips are welcome, my experience with php can be counted in hours, not days or weeks! But I've done a little perl cgi before. Regards, Børge