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                                   Persitence
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Swapfile
The swapfile is used to record buffer changes. It signals that the file is
currently edited or that something went wrong. It is used for recovery of
unsaved changes

Undofile
Undofile are kept in the undodir. It keeps the record of undoable changes even
if the file was closed. Careful undofiles are not removed automatically and so
 can grow. It is recommended to clean it regularly.

Backup (writebackup)
Just before writing the buffer to the file. A backup of the original file is
made. If the write is complete the backup is deleted just after.
The backup can be kept by using 'backup' instead

See also 'patchmode'
