When non-empty the oldest version of a file is kept. This can be used to keep the original version of a file if you are changing files in a source distribution. Only the first time that a file is written a copy of the original file will be kept. The name of the copy is the name of the original file with the string in the 'patchmode' option appended. This option should start with a dot. Use a string like ".orig" or ".org". 'backupdir' must not be empty for this to work (Detail: The backup file is renamed to the patchmode file after the new file has been successfully written, that's why it must be possible to write a backup file). If there was no file to be backed up, an empty file is created. When the 'backupskip' pattern matches, a patchmode file is not made. Using 'patchmode' for compressed files appends the extension at the end (e.g., "file.gz.orig"), thus the resulting name isn't always recognized as a compressed file. Only normal file name characters can be used, "/*?[|<>" are illegal.