Toggle the Erase and Delete mode of the Backspace and Delete keys.
With a prefix argument ARG, enable this feature if ARG is
positive, and disable it otherwise. If called from Lisp, enable
the mode if ARG is omitted or nil.
On window systems, when this mode is on, Delete is mapped to C-d
and Backspace is mapped to DEL; when this mode is off, both
Delete and Backspace are mapped to DEL. (The remapping goes via
`local-function-key-map', so binding Delete or Backspace in the
global or local keymap will override that.)
In addition, on window systems, the bindings of C-Delete, M-Delete,
C-M-Delete, C-Backspace, M-Backspace, and C-M-Backspace are changed in
the global keymap in accordance with the functionality of Delete and
Backspace. For example, if Delete is remapped to C-d, which deletes
forward, C-Delete is bound to `kill-word', but if Delete is remapped
to DEL, which deletes backward, C-Delete is bound to
`backward-kill-word'.
If not running on a window system, a similar effect is accomplished by
remapping C-h (normally produced by the Backspace key) and DEL via
`keyboard-translate': if this mode is on, C-h is mapped to DEL and DEL
to C-d; if it's off, the keys are not remapped.
When not running on a window system, and this mode is turned on, the
former functionality of C-h is available on the F1 key. You should
probably not turn on this mode on a text-only terminal if you don't
have both Backspace, Delete and F1 keys.
See also `normal-erase-is-backspace'.