INT 15 - TopView - SEND MESSAGE - "SETESC" - SET ESCAPE ROUTINE ADDRESS
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 a 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


1512 - TopView - SEND MESSAGE - "SETESC" - SET ESCAPE ROUTINE ADDRESS