[Zope] Can't nest dtml-in using prefix ...

This won't work: <dtml-in qry_user_roles prefix="outer"> <dtml-in qry_roles> <dtml-if expr="outer_role==role"> Roles are matching </dtml-if> </dtml-in> </dtml-in> I get an error that says key error - outer_role doesn't exist. It doesn't matter if I prefix the inner dtml-in as well. (I've read it isn't necessary though) Why won't the prefix work for me?