This mode is used during an in-place upgrade, where the installer creates a backup of the files modified or newly introduced by you in the old installation into a .migrate.bkp.<old_version> backup directory and merges them into a new installation. This mode has been designed for the installer, but can be invoked by you too.
Note:
This mode must not be invoked by you if there are multiple .migrate.bkp.<version> directories under the <BASEDIR/smarts directory.