INS, CTRL+V
Insertmode
Toggles between insert mode and overtype mode. If overtype mode is on, the letter O appears on the status bar. The cursor can also change shape, depending on the Cursormode switch. See: Cursormode.
In insert mode, each character you type is inserted at the cursor. This insertion shifts the remainder of the line one position to the right.
In overtype mode, the character you type replaces the character at the cursor.
TruePWB is in insert mode.
FalsePWB is in overtype mode.