[Zope] Adding text properties of a ZClass to PrincipiaSearchSource

I created some custom ZClass objects to publish Press Releases and News Items on our website. Since the submitters are nontechnical the objects use a large text property (STX_body) to hold the main text in structured text format. How can I add this STX_body property to the PrincipiaSearchSource? I would like to keep the site search simple by just doing a lookup on the PrincipiaSearchSource index. I would hate to have to create additional queries for other objects I created. Regards, Frank