Compatibility: 3.0+
Expects: AH    59H
BX    0000H (need for 3.x and 4.x)
Returns: AX    extended error code (0 if no error has occurred)
BH    error class
BL    suggested action
CH    location (where the error occurred)
Info: Use this function to figure out what to do after a DOS function
failed because of an error.  You can use this:

  Inside an INT 24H Critical Error handler
  After any INT 21H DOS function which signals an error with CF
  After FCB-style functions which return AL=ffH means an error

See DOS Error Codes for a full listing of possible error codes,
classes, suggested actions, and loci that may be returned by this

Notes:   After an error, you get only on chance to call this fn.  After
one call, the error condition is unflagged and subsequent calls
won't return meaningful data.

  You can use fn 5D0aH to simulate an error or set your own
internal error codes.

Versions: This function is not available before 3.00.

With 2.x, when CF returns indicating an error, use your own
program logic to decide what action to take.

With 3.0+, when a function returns CF=1, Microsoft advises to
ignore the error code returned in AX, call this function, and
take the action suggested in BL.

See Also: Fn 5d0aH (set extended error)
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DOS Fn 59H: Get Extended Error Info