[Zope] dtml-with string

Hi all ! i am having a problem with dtml-with tag the problem is: i want to do a <dtml-with "PARENTS[0].location.place"> the problem is that instead of writing PARENTS[0].location.place i want to use a variable that is a built string: <dtml-call "REQUEST.set('location', 'PARENTS[0].location.' + dir)"> dir is a dtml-var which has the string place ! and then use something like: <dtml-with "_[location]"> does someone knows how to do this ?? I have tried tips in zope.org but unsucessfuly here's the zope error: Error Type: KeyError Error Value: PARENTS[0].location.place thank you all Nuno