diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog index 503212097d6..58349355a0b 100644 --- a/doc/lispref/ChangeLog +++ b/doc/lispref/ChangeLog @@ -1,3 +1,8 @@ +2009-04-11 Eli Zaretskii + + * 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 * syntax.texi (Syntax Table Functions): Document cons cell diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi index b017ce70704..a6c09cd0e30 100644 --- a/doc/lispref/display.texi +++ b/doc/lispref/display.texi @@ -1148,6 +1148,14 @@ object that belongs to a particular buffer, and has a specified 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,