At the top of the man page for 'tar', there are many references to the argument 'MEMBER' but then it's not defined anywhere.
It took quite a bit of reading before I was able to deduce that it must simply be some file/directory that's already inside an existing archive.
(Which finally explains why it's only available to the --list and --extract operations.)
It just sure would've been nice if it explicitly stated that at the beginning somewhere.
thanks.