Under a locking-based version control system (such as SCCS, and RCS
in its default mode), C-x v v does the following:
If the file is not locked, lock it and make it writable, so that you
can change it.
If the file is locked by you, and contains changes, commit the
changes. In order to do this, Emacs first reads the log entry for the
new revision. See Log Buffer.
If the file is locked by you, but you have not changed it since you
locked it, release the lock and makes the file read-only again.
If the file is locked by some other user, ask whether you want to
“steal the lock” from that user. If you say yes, the file becomes
locked by you, but a message is sent to the person who had formerly
locked the file, to inform him of what has happened.
These rules also apply when you use CVS in locking mode, except
that CVS does not support stealing a lock.