[Zope] Using Property Sheet Methods in Z Class

In a Z Class I am creating (the one I wrote about in http://www.zope.org/Members/lstaffor/zProperties) I have property sheet named "InstanceConstants" which contains a property "pub_date". When accessing an instance of that class, "pub_date" is clearly available in the namespace of the object. However, the property sheet method <dtml-if "hasProperty('pub_date')"> always returns FALSE. I presume that somehow I have to qualify "hasProperty" with "InstanceConstants", but after spending an hour trying to follow the Property Sheets and ZClasses code, I still haven't found the answer. Can anyone help? -- Thanks -- Loren