This variable determines whether or not keystrokes are inserted in front of
any existing text when the user types an entry. Set this variable to "1" (on,
true, yes) to enable insertion. The default value is "0" (off, false, no), which
causes typing to replace existing text.
The user can change the state of INSERT_MODE with various key actions. For example, pressing the "Insert" key can
enable insertion. This variable has no affect on Windows controls.