[Zope] newbie dtml-if/expr ?

(zope-2.1.6, rh6-linux) How come I can't do this: <dtml-if "var1 and var2"> <dtml-call somefuncNeedingVar1AndVar2> </dtml-if> ...or other obvious (e.g. (extra) (parenthesized)) variations thereupon, but the following seem to work: <dtml-if "_.has_key('var1') and _.has_key('var2')"> ... </dtml-if> ...or this... <dtml-if "_.has_key('var1') and _.var2"> <!-- but not vice-versa --> ... </dtml-if> ...or even worse, this... <dtml-if var1> <dtml-if var2> ... </dtml-if> </dtml-if> Can't seem to find the answer in the zqr or dtml reference... what am I missing here? Hopefully there's a simple answer. :) Many thanks, -Dan