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INT 7A - IBM 3270 Workstation Program API - WINDOW SERVICES
        AH = 09h
        BX = 8020h (synchronous request)
        CX = 00FFh
        DX = ID of window service controller (WSCTRL)
        AL = service
            01h connect to WS control
            02h disconnect from WS control
            03h add a window
            04h change window's position on screen
            05h change window's size
            06h change window's color
            07h change window's position in the presentation space
            08h hide/unhide toggle
            09h enlarge/reduce toggle
            0Ah change screen background color
            0Bh get window's position on screen
            0Ch get window's size
            0Dh get window's color
            0Eh get window's position in the presentation space
            0Fh determine whether hidden
            10h determine whether enlarged
            11h get background color
            12h get window names
            13h delete all windows from profile
            14h pick active window
            15h redraw screen
            16h redraw window
            17h delete a window from profile
            18h get active window
            19h get active screen
            1Ah get window data
            1Bh change window data
            1Ch select active screen
        ES:DI -> control block
Return: ???