method added to support tabs
  return the line after the "\t" are replaced with the correct
  amount of spaces

#
  Clear the checked selections.

draw(N, left_pos, yp, i)

#
  This method is overridden by the subclass to draw the given
  line at the given position
  @param N  The object to be drawn
  @param left_pos  The left position it should be drawn at
  @param yp   The y position it should be drawn at
  @param i   The index into the data corresponding to N

get_checked()

#
  Get the checked lines.
  @return A list corresponding to the data.  If an element is not {&null}, then
  @ the corresponding line is checked.

#
  Return the contents of the {ScrollArea}

 Present page size

#
 Return the item previously under the clicked cursor
 @return The item number

#
  Return a list of items checked (highlighted)
  @return A list of items currently checked

#
 Return item currently under the clicked cursor
 @return The item number

 Goto line, pos

handle_key_down(e)

handle_press(e)

  helper method for actual_line

#
 Return object currently under the clicked cursor
 @return The object

#
  Return a list of objects checked (highlighted)
  @return A list of objects currently checked

#
 Return object currently under the clicked cursor
 @return The object

#
  Set the current selections to the list l, which is a list of objects
  @param l  The list of objects.

 Re-draw the text area.  Use double-buffering to avoid flicker.

set_checked(l)

#
  Set the checked (highlighted) lines.
  @param l   A list.  Each element in the list corresponds to an element in
  @ the data.  If the element is not {&null}, the line is checked.

#
  Set the data to be displayed.
  @param x  The list of data.

 Called on resize, buttons resized, or contents amended

#
 Configure the object so that several lines may be highlighted

#
 Configure the object so that only one line may be highlighted

#
  Set the current selections to the list l, which is a list of
  item numbers.
  @param l   The list of item numbers.