Commit b20ecfa1 authored by Eli Zaretskii's avatar Eli Zaretskii
Browse files

(Overlays): Overlays don't scale well. See
parent cd093dcf
2009-04-11 Eli Zaretskii <>
* display.texi (Overlays): Overlays don't scale well. See
2009-04-10 Chong Yidong <>
* syntax.texi (Syntax Table Functions): Document cons cell
......@@ -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,
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