[Zope] dtml-with string

[nuno]

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