terminal (1985) introduced an "INSERT HERE" key in the editing key group. It would send the escape sequence "CSI 2 ~" to the host. In return, a host application could send "CSI 4 h" or "CSI 4 l" to switch Insert/Replace Mode (IRM) on the terminal.

XTerm, a terminal emulator for the X Window System, sends "CSI 2 ~" in DEC mode, "CSI 2 z" in Sun mode,