VT100: KP.                  VT200: KP.
    DEFINE_KEY Function: EXTEND

    Used in conjunction with another key, allows access to an
    extended function for that key. First invoke the EXT function,
    and then press the second key. If you invoke EXT accidentally,
    invoke the RESET function to cancel the EXT function.

    If the status display is enabled when you invoke the EXT
    function, the word Extend appears on the status line.