Understanding virtual mailboxes (examples in 15-mailboxes.conf)

[MRob]

The examples in 15-mailboxes.conf

# If you have a virtual "All messages" mailbox:
   #mailbox virtual/All {
   #  special_use = \All
   #  comment = All my messages
   #}

   # If you have a virtual "Flagged" mailbox:
   #mailbox virtual/Flagged {
   #  special_use = \Flagged
   #  comment = All my flagged messages
#}

They seem to reference some kind of virtual mailbox setup that doesn't 
compare to the docs for the "virtual" plugin. That plugin says we should 
create a separate namespace instead, like "namespace virtual" and put 
files representing the virtual folders into user maildirs. What if we 
use mdbox? add the files to user/mailboxes director I will guess.

Is there a way to use the mailbox examples in the inbox namespace in the 
default config? Does it use some other method different from the virtual 
plugin? maybe more config hints for those examples would be helpful.

Thank you.