[Dovecot] Basic namespaces question

[David King]

I can't find a generalised "What the heck are namespaces all about?" anywhere, can anyone point me to a decent one?

More directly, my question is this: if I set up two non-hidden private namespaces (one for mbox and one for maildir), will a well-written IMAP client automagically list folders from both as if they were part of (or below) the same hierarchy, or do I have to set up two accounts, one with a prefix of (say) #mbox and one of #maildir?

One step further, I'd like to eventually get mail from /var/mail/%u in mbox format, and in "maildir:%h/.maildir" or "mbox:%h/.mail", whichever exists (I'm migrating from imap-uw, and would like the benefits of maildir without forcing users to change their mailstores in case they use pop3 or tools like mail(1)). I'm willing to do some coding for it, but I imagine that it would be non-trivial if namespaces aren't automatically integrated