KEY enables, disables, or suspends event trapping of a key.
If event trapping is enabled, ON KEY branches to a subroutine whenever
the key is pressed.
 
KEY(n%) ON
KEY(n%) OFF
KEY(n%) STOP
ON KEY(n%) GOSUB line
 
    - n%              A value that specifies a function key, direction key,
                      or user-defined key:
 
                      n%        Key
                      ------    --------------------------------------------
                      0         All keys listed here (KEY(0) ON, KEY(0) OFF,
                                and KEY(0) STOP only).
                      1-10      Function keys F1-F10.
                      11        Up Arrow key.
                      12        Left Arrow key.
                      13        Right Arrow key.
                      14        Down Arrow key.
                      15-25     User-defined keys. For more information,
                                see <DECLARING USER-DEFINED KEYS>.
                      30, 31    Function keys F11 and F12.
 
    - KEY(n%) ON      Enables event trapping for the specified key.
    - KEY(n%) OFF     Disables key event trapping.
    - KEY(n%) STOP    Suspends key event trapping. Events are processed
                      once event trapping is enabled by KEY ON.
    - line            The label or number of the first line of the
                      event-trapping subroutine.
 
Example:
    'This example requires Caps Lock and Num Lock to be off.
    CONST ESC = 27
    KEY 15, CHR$(&H4) + CHR$(&H1F)              'Set up Ctrl+S as KEY 15.
    ON KEY(15) GOSUB PauseHandler
    KEY(15) ON
    WHILE INKEY$ <> CHR$(ESC)
        PRINT "Press Esc to stop, Ctrl+S to pause."
        PRINT
    WEND
    END
 
    PauseHandler:
        SLEEP 1
        RETURN
 
See Also    <KEY (ASSIGNMENT)>    <DECLARING USER-DEFINED KEYS>