Int 2F Fn 0500  U - Dos 3.0+ Critical Error Handler - Installation Check   [l]

   AX = 0500h

Return: AL = status
       00h not installed, OK to install
       01h not installed, can't install
       FFh installed
   BX destroyed (MSCDEX v2.21-2.25)
   CF clear (MSCDEX v2.21-2.25)
Desc:  determine whether a critical error message override is installed

Note:  this set of functions allows a user program to partially or completely
     override the default critical error handler's message in COMMAND.COM

See Also: AH=05h,INT 24