Syntax:  COLLAPSE depth

  Compresses text and displays an overview at the current cursor
  position.

  Low-level detail lines are replaced by a single overview line.  The
  cursor position is recorded before the text is collapsed for use with
  future EXPAND commands.  The editor determines the relative level of
  detail of a line by comparing the indentation of the line with the
  indentation of other lines.  The editor's treatment of the
  indentation of a line is influenced by indentation adjustment
  definitions.  For more information, see the ADJUSTMENT command.