[Zope] Q: Howto create a different tree element ?

I need a navigation element for tree-like structures, but with a different rendering (no collapsing/expanding, different font sizes for the various depths etc.). I could try and write that thing from scratch, but given that most of its interface is similar to the TreeDisplay code, I wonder what would be the zopisticated way to reuse the interface and as much code as possible. Perhaps a similar question is: given that TreeDisplay is a builtin DTML tag, should I try to augment the TreeDisplay code, or is there a reasonable way to build user-defined DTML tags, or is it more reasonable to employ traditional methods (e.g. var-exprs) for this ? Gregor