[Zope] dtml-tree info

Hope someone has already run into this: I need to be able to control the tree display state from dtml and I can't find any info on the subject. The "normal" tree display has the "+" (or "-") part, with its own URL that includes an encoded argument, and the user-defined part. At the very least I would like to be able to mimic the behaviour of the "+" by clicking on the "user" part (which I make into a link by myself). To make matters worse, this link may take me to another object (page). Ideally, I would like to be able to control the display behaviour - saying which branch(es) are to be shown open and which closed, and to which level, within the page itself. Any pointers would be greatly appreciated. Tnx, Robert