[Zope] dynamically changing a tree icon?

For example, a person is browsing a site that uses a dtml tree for navigation and I want to change the icon for the node to a different icon (say, that shows a checkmark) when they have visited the page (or interacted with it in some way). what would be the best way to do this? ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com