INT 33h,  10h (16)       Conditional Off

    Defines an area where the mouse cursor is invisible.

       On entry:      AX         10h
                      CX         Upper X Screen Coordinate
                      DX         Upper Y Screen Coordinate
                      SI         Lower X Screen Coordinate
                      DI         Lower Y Screen Coordinate

       Returns:       Nothing

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    Function 10h defines a region on the screen for updating.

    If the mouse pointer is in the defined region or moves into it, function
    10h hides the mouse cursor while the region is being updated. After Your
    program calls function 10h, it must call function 1 later on to show the
    cursor again.

    The rigion is defined by placing the screen coordinate values in the
    four parameter registers. The CX and DX registers define the upper left
    corner of the region; the SI and DI registers define the lower right
    corner.

    Function 10h is similar to function 2 but is intended for advanced
    applications that require quicker screen updates.