Int 15 Fn 12  - Topview - Send Message - "setesc" - Set Escape Routine Ad  [Q]

   AH = 12h
   BH = 14h
   BL = message modifier
       00h handle is DWORD on top of stack
       01h define user stream
       04h intercept keystrokes from KEYBOARD to window (handle on stack)
       05h intercept keystrokes from task's default KEYBOARD to a window
   STACK: (if window)   DWORD user stream number (14h-1Fh)
                DWORD address of FAR user stream handler
          (if keyboard) DWORD address of FAR filter function

The keyboard filter function is called when the keyboard is in field mode.  On
entry,
   AL = character
   AH = 00h or extended ASCII code if AL = 00h
   BL = field number
   CH = cursor column
   CL = cursor row
   DL = field type modifier (sixth item in field table entry)
   DH = seventh item in field table entry
   ES:SI = window's handle
   DS:DI -> field table entry for field containing the cursor
The filter function should return
   AH = 00h use keystroke
        01h ignore keystroke
        FFh beep and ignore keystroke

Note: the filter function is not allowed to make INT 15, DOS, or BIOS calls