overwrite-mode

overwrite-mode is a variable defined in `C source code'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Non-nil if self-insertion should replace existing text.
The value should be one of `overwrite-mode-textual',
`overwrite-mode-binary', or nil.
If it is `overwrite-mode-textual', self-insertion still
inserts at the end of a line, and inserts when point is before a tab,
until the tab is filled in.
If `overwrite-mode-binary', self-insertion replaces newlines and tabs too.