[Zope-dev] Computed fields in ZCatalog

Hi, Looking at the ZCatalog code, if an index or metadata field is callable for a particular object, then that function will be called. However, it isn't called with *any* parameters. Is there any way to make that metadata value based upon other values in the object? For example, if I wanted to create a method that would return Property1+Property2 and have that value show up in the Catalog, can that be done? Kevin