[Zope] Storing documents and metadata (associated XML fragment)

Hello, I want to store some kind of library of arbitrary files (similar to the file library example in the distribution). Further, I'd like to store an associated XML fragment (metadata) with the document. This XML fragment should be accessible externally, via XML-RPC for example. What is the best way to store such things in Zope? Would I store Metadata in separate files along with the original files? Or should I extend the File with a string member to hold metadata (may be large, though)? Any other suggestions? Thanks in advance, Lars