[Zope] Acquire variable for ZCatalog indexing?

[Art Hampton]

I asked this previously, and got no replies.  I'll give it one more
shot.

When making a Z Catalog of a certain class of object, is it possible to
acquire a variable from parent objects?

I'd like to define category_id as a property of a folder, and then have
my Z Catalog pick up that property when it is indexing the objects in
the folder.

Is this currently possible?  If not, wouldn't it be a handy enhancement?
:)