* lisp.h (Lisp_Overlay): New tag.

	(OVERLAYP): New predicate.
	(CHECK_OVERLAY): New type-checker.
	(Qoverlayp): New extern declaration.
	* buffer.c (Foverlayp): New function.
	(Qoverlayp): New atom.
	(overlays_at, recenter_overlay_lists): Abort if we encounter an
	invalid overlay.
	(syms_of_buffer): defsubr Soverlayp; initialize Qoverlayp.
	(Fdelete_overlay): Set the overlay's markers to point nowhere.
	Use CHECK_OVERLAY instead of signalling a special error.
	(Fmove_overlay, Foverlay_put): Use CHECK_OVERLAY instead of
	signalling a special error.
	(Foverlay_get): Use CHECK_OVERLAY.
	* fns.c (internal_equal): Define this for overlays.
	* buffer.h (OVERLAY_VALID): Define in terms of OVERLAYP.
	* print.c (print): Give overlays their own print syntax.
	* alloc.c (mark_object): Treat overlays like conses.

1 files changed, 1 insertions, 2 deletions

diff --git a/src/buffer.h b/src/buffer.h
index 34d92fd61c7..3ab666c07bf 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -370,7 +370,7 @@ extern Lisp_Object Vtransient_mark_mode;
    Therefore, we cannot assume that they remain valid--we must check.  */
 
 /* 1 if the OV is a cons cell whose car is a cons cell.  */
-#define OVERLAY_VALID(OV) (CONSP ((OV)) && CONSP (XCONS ((OV))->car))
+#define OVERLAY_VALID(OV) (OVERLAYP (OV))
 
 /* Return the marker that stands for where OV starts in the buffer.  */
 #define OVERLAY_START(OV) (XCONS (XCONS ((OV))->car)->car)
@@ -386,7 +386,6 @@ extern Lisp_Object Vtransient_mark_mode;
  ((MARKERP ((P)) && XMARKER ((P))->buffer == current_buffer)    \
   ? marker_position ((P)) : 0)
 
-
 /* Allocation of buffer text.  */
 
 #ifdef REL_ALLOC