INT 11 - RainbowFAX v1.3 - SFENGINE API - ???
        AH = 79h
        AL = subfunction
            01h set ??? flag
                Return: AX = previous state (0000h already set, 0001h clear)
            02h clear ??? flag (see subfunc 01h)
                Return: AX = 0001h
            03h set ??? flag (different from subfn 02h or 04h)
                Return: AX = 0001h
            04h clear ??? flag (different from subfn 02h or 03h)
                Return: AX = 0001h
            else
                Return: AX = FFFFh
SeeAlso: AH=77h,AH=78h,AH=7Ah,AH=7Ch

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