Vista Tutorial - WLM and IMAP deleted items

One option under Tools / Options / Advanced is "Use the 'Deleted Items'
folder for IMAP accounts".
This could mean either:
a. When I delete an email from my IMAP Inbox, move it to the Deleted Items
folder which lives under (local) Storage folders. If so, this presumably (?)
means COPY it there (and which from thenceforth becomes a local copy) and
then issue a purge command for the IMAP master version
or
b. When I delete an email from my IMAP Inbox, move it to the IMAP folder for
deleted items. This folder is called whatever the IMAP server wants to call
it: it may be Trash, Deleted Items or something else. This means it stays
within IMAP and the version in Trash (or whatever) remains a cached version
of the master version held centrally.

Since the first is local (outside IMAP) and the other remote (but cached
locally), there is a big difference in how they are handled.

DAK which is it pls?