INT 11 - RainbowFAX v1.3 - SFENGINE API - ???
        AH = 7Ch
        AL = subfunction
            01h set ??? flag (see also subfn 02h)
                Return: AX = 0001h
            02h clear ??? flag (see also subfn 01h)
                Return: AX = 0001h
            else
                Return: AX = FFFFh
SeeAlso: AH=77h,AH=78h,AH=79h,AH=7Ah

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