Int 10h, 07h            Scroll Window Down

    Scrolls a specified window downward a specified number of lines.

        Entry   AH = 07h
                AL = Number of lines to scroll (if 0, clear entire window)
                BH = Display attribute for blank lines
                CH = Row number of upper left corner
                CL = Column number of upper left corner
                DH = Row number of lower right corner
                DL = Column number of lower right corner

        Return  Nothing

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    Lines are inserted at the top with all lines moving down. The new
    lines are filled with blank characters of a specified display
    attribute (value in BH). The lines that disappear at the bottom of
    the window are lost.