INT 10H 07H: Scroll Down / Clear Screen Rectangle

                                                          Compatibility: All
 Expects: AH    07H
          AL    number of lines to scroll in (0=blank entire rectangle)
          BH    video attribute to be used on blank line(s)
          CH,CL row,clm of lower-right corner of rectangle to scroll/blank
          DH,DL row,clm of upper-left corner of rectangle to scroll/blank
 Returns: (none)
    Info: You may use this to scroll screen text down; that is, move each
          line of text lower on the screen and add one or more blank lines
          at the top.

          This fn can be used to scroll a rectangular subset of the screen.
          It may also be used to clear the entire screen or any rectangular

          See INT 10H 06H (scroll up / cls) for notes and related info.

See Also: INT 10H 06H (scroll up / cls)
          INT 10H: Video Services