[Dovecot] What does "namespace inbox {..." mean

[Jonathan Ryshpan]

I'm trying to set up a dovecot server for which mail arrives in an mbox,
and mail is stored in a maildir.  The wiki (see
http://wiki.dovecot.org/Namespaces) refers to this as "Mixed mbox and
Maildir".  It advises handling this situation by creating two
namespaces: one for the mbox and the other for the maildir. On the other
hand the sample configuration coming with dovecot in my distro puts
inbox in a namespace starting with:
        namespace inbox {
          # Namespace type: private, shared or public
          #type = private

It appears from the wiki that the word following the namespace
declarator (if this is the right word) should be either "public",
"shared", or "private", and describes a property of the namespace being
declared.  So what does:
        namespace inbox {...
mean?  Similarly in another part of the wiki (see
http://wiki2.dovecot.org/Plugins/Virtual), I read that it's possible
to have
        namespace virtual {
        namespace real {
	...
which only increases my perplexity.

Please advise!

Thanks - jon