NAME
    CBD_CHANGEHOOK -- Add or remove a clip change hook

FUNCTION
    CBD_CHANGEHOOK allows specification of a hook to be called
    when the data on the clipboard has changed.

IO REQUEST
    io_Message      mn_ReplyPort set up
    io_Device       preset by opendevice
    io_Unit         preset by opendevice
    io_Command      CBD_CHANGEHOOK
    io_Length -     0 to remove, 1 to install this hook
    io_Data -       struct hook *, the clip change hook

HOOK ENVIRONMENT
   hook message - a cliphookmsg, as defined in devices/clipboard.h
       chm_Type - 0, indicating that the message has the
           following fields:
       chm_ClipID - the clip ID of the clip triggering the change
   hook object - io_Unit