From xemacs-m  Sun Apr  6 16:02:44 1997
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From: Kyle Jones <kyle_jones@wonderworks.com>
To: XEmacs Developers <xemacs-beta@xemacs.org>
Subject: Value of overlay.el
In-Reply-To: <kig3et4lz62.fsf_-_@jagor.srce.hr>
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	<kig3et4lz62.fsf_-_@jagor.srce.hr>
X-Mailer: VM 6.24 under 19.15 XEmacs Lucid
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Hrvoje Niksic writes:
 > Kyle Jones <kyle_jones@wonderworks.com> writes:
 > 
 > > More overlay.el lossage and again it is VM's fault for inadvertently
 > > mixing the extent/overlay interfaces.  Fixed in VM 6.24.
 > 
 > Finally, how does `overlay.el' scale up, in your opinion (with the
 > list->cons change made, of course)?  Is it still on the `oboy' level,
 > or is it a usable emulation of GNU Emacs overlay mechanism?

Quite usable if your goal is to change display characteristics.

There are problems if you rely on the "overlay endpoints are
markers" feature of GNU Emacs.  insert-before-marker at the
start/end of an overlay always moves the start/end point.  This
is not true for XEmacs extents.  This means using the emulated
overlays for delimiting text regions might yield surprising
results in some cases.

The overlay emulation won't at all if you want to use overlay
modification hooks; that would require C code changes.

