SQL Backend for IMAP METADATA Dictionary

I've seen documentation on using a SQL backend for quota dictionary and passdb&userdb dictionary. However, I can't find any examples of a SQL backend for IMAP METADATA / mail_attributes_dict.

Is this combination possible? If so, is there an example somewhere?

I am unsure what data structures it's expected or how to create the map entries for it.

Thanks in advance.

Joseph D. Wagner