30.1.3.3 Advanced Control in C-x v v

When you give a prefix argument to vc-next-action (C-u C-x v v), it still performs the next logical version control operation, but accepts additional arguments to specify precisely how to do the operation.

• You can specify the name of a version control system. This is useful if the fileset can be managed by more than one version control system, and Emacs fails to detect the correct one.
• Otherwise, if using CVS, RCS or SRC, you can specify a revision ID.

  If the fileset is modified (or locked), this makes Emacs commit the files with that revision ID. You can create a new branch by supplying an appropriate revision ID (see Version Control Branches).

  If the fileset is unmodified (and unlocked), this checks out the specified revision into the working tree. You can also specify a revision on another branch by giving its revision or branch ID (see Switching between Branches). An empty argument (i.e., C-u C-x v v RET) checks out the latest (a.k.a. “head”) revision on the current branch.

  Specifying revision ID in this manner is silently ignored by a decentralized version control system. Those systems do not let you specify your own revision IDs, nor do they use the concept of checking out individual files.