[Zope] Date and Zclass properties

Hi, I'd like to put a date as a property of my Zclass but I have many trouble to find a correct format for it. I think I can also use string, int or float. But it's not perfect: How can I use all the methods for the DateTime Class with this property ? I'd like to store a date of publication in this property and to be able to sort instances by this date (different than bobobase_modif). And also to be able to use the format I want for the date. Benoît... Benoît DOMINIAK 40, rue Colin 69100 Villeurbanne FRANCE tél. : +33 (0)608463826 Fax : +33 (0)478931865