[Zope] date arithmetic in DTML

how can I datearithmetic in DTML for example today - 30 days, to search for a date in a db, which is not older than today - 30 days. Where can I find documentation about it ? Gruß Joachim Schmitz WWW-Consultant email: js@ac-copy.net tel: +49-241-89491-0 fax: +49-241-89491-29