{only when compiled with the |+persistent_undo| feature} List of directory names for undo files, separated with commas. See |'backupdir'| for details of the format. "." means using the directory of the file. The undo file name for "file.txt" is ".file.txt.un~". For other directories the file name is the full path of the edited file, with path separators replaced with "%". When writing: The first directory that exists is used. "." always works, no directories after "." will be used for writing. When reading all entries are tried to find an undo file. The first undo file that exists is used. When it cannot be read an error is given, no further entry is used. See |undo-persistence|. This option cannot be set from a |modeline| or in the |sandbox|, for security reasons.