portupgrade "---> Backing up the old version"

[E. J. Cerejo]

While using portupgrade I noticed before it deinstalls the old port it 
says something like "--->  Backing up the old version" and then it goes 
on deinstalling and installing the new version.  Where does this backup 
go?  I looked at the man page and it says something like /var/tmp but I 
went into that directory and there is nothing in there relating to a 
port back!  Does portupgrade delete that backup after the successful 
install of the new version?

Thanks.