+2009-04-11 Eli Zaretskii <eliz@gnu.org>
+
+ * display.texi (Overlays): Overlays don't scale well. See
+ http://lists.gnu.org/archive/html/emacs-devel/2009-04/msg00243.html.
+
2009-04-10 Chong Yidong <cyd@stupidchicken.com>
* syntax.texi (Syntax Table Functions): Document cons cell
beginning and end. It also has properties that you can examine and set;
these affect the display of the text within the overlay.
+@cindex scalability of overlays
+The visual effect of an overlay is the same as of the corresponding
+text property (@pxref{Text Properties}). However, due to a different
+implementation, overlays generally don't scale well (many operations
+take a time that is proportional to the number of overlays in the
+buffer). If you need to affect the visual appearance of many portions
+in the buffer, we recommend to use text properties.
+
An overlay uses markers to record its beginning and end; thus,
editing the text of the buffer adjusts the beginning and end of each
overlay so that it stays with the text. When you create the overlay,