23.7.3.3 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.

• If the file is modified (or locked), you can specify the version number to use for the new version that you check in. This is one way to create a new branch (see Branches).
• If the file is not modified (and unlocked), you can specify the version to select; this lets you start working from an older version, or on another branch. If you do not enter any version, that takes you to the highest version on the current branch; therefore C-u C-x v v <RET> is a convenient way to get the latest version of a file from the repository.
• Instead of the version number, you can also specify the name of a version control system. This is useful when one file is being managed with two version control systems at the same time (see Local Version Control).