Int 2F Fn 05  CU - DOS 3+ Critical Error Handler - Expand Error Into Stri  [l]

   AH = 05h
---DOS 3.x---
   AL = extended error code (not zero)
---DOS 4+ ---
   AL = error type
       01h DOS extended error code
       02h parameter error
   BX = error code

Return: CF clear if successful
       ES:DI -> ASCIZ error message (read-only)
       AL = completion state
       00h message requires completion with device name, drive, etc.
       01h message is complete as returned
   CF set if error code can't be converted to string
       AX,DI,ES destroyed
   other flags corrupted

Notes: called at start of COMMAND.COM's default critical error handler if
     installed by a user program, allowing partial or complete overriding
     of the default error messages
   subfunction 02h is called by many DOS 4 external programs
   DR-DOS's COMMAND.COM appends additional info ("0 files copied") to the
     returned string

See Also: AX=0500h,AX=122Eh,INT 24