Function            scroll_down - scroll window down

  Syntax              void scroll_down(int left, int top, int right,
                                       int bottom);

  Prototype in        video.h

  Remarks             scroll a box, delineated by the coordinates, down 1
                      line. A blank line will be inserted at the top, and
                      the bottom line will be lost. The scrolling is done
                      via INT 0x10, Function 7. Coordinates are absolute.

  Return value        nothing.

  See also            scroll_up()

  Example             #include <video.h>

                      main()
                      {
                           scroll_down(0,0,4,79);
                           /* scroll bottom 4 lines */
                      }