[Zope] Me vs. The Zope Book Pt. 1

I can't get some of the things mentioned in the ZB to work as expected. If anyone could tell me what I'm doing wrong, that'll be much appreciated. 1. The following code - <dtml-tree> <dtml-var getId> </dtml-tree> gives me nothing! Even in root, when I'm logged in as site manager, & when I'm an authenticated user, when the script has a proxy role of Manager, when it doesn't, etc. According to ZB (pg. 124) I should see a display of an HTML tree. What am I missing? Samir