[Zope] boolean search

Dear all, Even though it seems so basic, I could't find a single reference to this problem. I'm trying to list some objects of a given meta_type based on some booleans they *might* have. For example: <dtml-in "Catalog.searchResults({'meta_type':'whatever','published':'1'})"> While a missing boolean property (¿always?) means "off", there's often arbitrary values when in "on" state, mainly depending on how the input was set in the form. So the question is: how should the query be set to bring only those items that DO have a certain property? TIA, Pablo