[Zope] 'summary' metadata in ZCatalog

[a32955@pop-server.nc.rr.com]

By default, ZCatalog creates a few metadata elements: id, title, summary, 
bobobase_modification_time, etc.

In the results objects returned by a search of my site, the 'summary' 
metadata is always blank.  The other metadata elements always have 
something store in them, but 'summary' is always blank.  How do I get 
ZCatalog to store a summary of each object during indexing?

Thanks for any replies.

Joe