*** add-to-invisibility-spec, remove-from-invisibility-spec<BR>
Modes that use overlays to hide portions of a buffer should set the
invisible property of the overlay to the mode's name (or another symbol) 
and modify the `buffer-invisibility-spec' to include that symbol. 
Use  `add-to-invisibility-spec' and `remove-from-invisibility-spec' to
manipulate the `buffer-invisibility-spec'. 
Here is an example of how to do this:
<P>
 ;; If we want to display an ellipsis:
 (add-to-invisibility-spec '(my-symbol . t)) 
 ;; If you don't want ellipsis:
 (add-to-invisibility-spec 'my-symbol) 
<P>
  ...
 (overlay-put  (make-overlay beginning end)  'invisible 'my-symbol)
<P>
 ...
 ;; When done with the overlays:
 (remove-from-invisibility-spec '(my-symbol . t))
 ;; Or respectively:
 (remove-from-invisibility-spec 'my-symbol)
<P>