[Zope] How to clean a vocabulary

Hi, do vocabulary objects delete a word that is not referenced anymore (I don´t think so)? If not, how can I programatically clean a vocabulary object inside a ZCatalog, I mean, delete all (or some specific) words that are not in use anymore? One more question: is there a size limit or number of objects limit one can store in a folder hierarchy, or the limit for Zope is only the data.fs limit? regards, Rogerio Atem