Syntax:  SET SCROLL MARGINS top_margin bottom_margin

  Specifies the lines at the top and bottom of the buffer at which the
  cursor triggers scrolling.

  This command sets the scroll lines at which scrolling is triggered by
  moving the cursor to these lines.  The scroll margins you set apply
  to all windows in the current editing session.  You specify the
  number of lines up from the top of the window or down from the bottom
  of the window at which you want scrolling to begin.  You can
  optionally specify scroll margins as percentages of the window
  height.

  The following example sets the scroll margins at two lines from the
  top and three lines from the bottom of all windows in the current
  editing session:

  LSE> SET SCROLL MARGINS 2 3

  This example sets the scroll margins at 10% from the top and 15% from
  the bottom of all windows in the current editing session:

  LSE> SET SCROLL MARGINS 10% 15%