start	allow backspacing over the start of insert; CTRL-W and CTRL-U
		stop once at the start of insert.
	nostop	like start, except CTRL-W and CTRL-U do not stop at the start of
		insert.

	When the value is empty, Vi compatible backspacing is used, none of
	the ways mentioned for the items above are possible.

				*'backup'* *'bk'* *'nobackup'* *'nobk'*
'backup' 'bk'		boolean	(default off)
			global
	Make a backup before overwriting a file.  Leave it around after the
	file has been successfully written.  If you do not want to keep the
	backup file, but you do want a backup while the file is being
	written, reset this option and set the 'writebackup' option (this is
	the default).  If you do not want a backup file at all reset both
	options (use this if your file system is almost full).  See the
	|backup-table| for more explanations.
	When the 'backupskip' pattern matches, a backup is not made anyway.
	When 'patchmode' is set, the backup may be renamed to become the
	oldest version of a file.

						*'backupcopy'* *'bkc'*
'backupcopy' 'bkc'	string	(default "auto")
			global or local to buffer |global-local|
	When writing a file and a backup is made, this option tells how it's
	done.  This is a comma-separated list of words.

	The main values are:
	"yes"	make a copy of the file and overwrite the original one
	"no"	rename the file and write a new one
	"auto"	one of the previous, what works best

	Extra values that can be combined with the ones above are:
	"breaksymlink"	always break symlinks when writing
	"breakhardlink"	always break hardlinks when writing

	Making a copy and overwriting the original file:
	- Takes extra time to copy the file.
	+ When the file has special attributes, is a (hard/symbolic) link or
	  has a resource fork, all this is preserved.
	- When the file is a link the backup will have the name of the link,
	  not of the real file.

	Renaming the file and writing a new one:
	+ It's fast.
	- Sometimes not all attributes of the file can be copied to the new
	  file.
	- When the file is a link the new file will not be a link.

	The "auto" value is the middle way: When Vim sees that renaming the
	file is possible without side effects (the attributes can be passed on
	and the file is not a link) that is used.  When problems are expected,
	a copy will be made.

	The "breaksymlink" and "breakhardlink" values can be used in
	combination with any of "yes", "no" and "auto".  When included, they
	force Vim to always break either symbolic or hard links by doing
	exactly what the "no" option does, renaming the original file to
	become the backup and writing a new file in its place.  This can be
	useful for example in source trees where all the files are symbolic or
	hard links and any changes should stay in the local source tree, not
	be propagated back to the original source.
								*crontab*
	One situation where "no" and "auto" will cause problems: A program
	that opens a file, invokes Vim to edit that file, and then tests if
	the open file was changed (through the file descriptor) will check the
	backup file instead of the newly created file.  "crontab -e" is an
	example, as are several |file-watcher| daemons like inotify.  In that
	case you probably want to switch this option.

	When a copy is made, the original file is truncated and then filled
	with the new text.  This means that protection bits, owner and
	symbolic links of the original file are unmodified.  The backup file,
	however, is a new file, owned by the user who edited the file.  The
	group of the backup is set to the group of the original file.  If this
	fails, the protection bits for the group are made the same as for
	others.

	When the file is renamed, this is the other way around: The backup has
	the same attributes of the original file, and the newly written file
	is owned by the current user.  When the file was a (hard/symbolic)
	link, the new file will not!  That's why the "auto" value doesn't
	rename when the file is a link.  The owner and group