* display.texi (Managing Overlays): Document copy-overlay (Bug#4549).

doc/lispref/ChangeLog

+2009-09-25  David Engster  <deng@randomsample.de>
+
+	* display.texi (Managing Overlays): Document
+	copy-overlay (Bug#4549).
+
 2009-09-22  Glenn Morris  <rgm@gnu.org>
 
 	* internals.texi (Building Emacs): Mention preloaded-file-list.

doc/lispref/display.texi

@@ -1267,6 +1267,14 @@ the specified region.  If @var{start} and/or @var{end} are omitted or
 @code{nil}, that means the beginning and end of the buffer respectively.
 Therefore, @code{(remove-overlays)} removes all the overlays in the
 current buffer.
+@end defun
+
+@defun copy-overlay overlay
+This function returns a copy of @var{overlay}.  The copy has the same
+endpoints and properties as @var{overlay}.  However, the marker
+insertion type for the start of the overlay and for the end of the
+overlay are set to their default values (@pxref{Marker Insertion
+Types}).
 @end defun
 
   Here are some examples: