Or maybe I'm just going at this from the wrong direction. On the page I'm setting up, users can either buy individual tracks or a whole album (a single zip file of all the tracks).
If the user adds the album item to the cart, then returns to the page and adds individual tracks from the same album to the cart, the cart will then hold the entire album PLUS whatever individual tracks he just added.
Ideally, I'd be able to make my page smart enough that it wouldn't add individual tracks to the cart if the album was already in there.
And I guess the inverse is also true... if the user adds individual tracks, then goes back and adds the album, I'd like to remove the individual tracks leaving only the newly-added album.
Any ideas about how to approach this?