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Re: Info mutilates user overlays.

From: Stefan Monnier
Subject: Re: Info mutilates user overlays.
Date: 01 Oct 2003 13:33:45 -0400
User-agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3.50

> this one, related to the same fact.  Position registers get treated
> exactly like overlays and hence are unusable.  Bookmarks at first seem
> to work, but malfunction.  After you save one bookmark, say in
> (emacs)Secondary Selection, then all subsequent bookmarks in different
> Info files get saved under "Secondary Selection".  The user believes

These are bugs (or at least misfeatures).  Patches welcome.

> In as far as Miles' question is concerned, I am using overlays to
> highlight regions with a non-nil text or overlay property, but I
> sometimes use overlays to highlight all kinds of stuff.  I can always
> rehighlight.  That is somewhat inconvenient, but less inconvenient
> than the register-bookmark stuff.

How do you highlight?  What do you highlight?  What for?

> There is one more problem with that overlay repositioning.  Maybe it
> applies to *Help* buffers as well.  Unreferenced deleted overlays are
> inaccessible (in as far as I know) and hence are garbage, which (I
> would guess) gets garbage collected.  But these repositioned overlays,
> even if unreferenced, remain accessible through (overlays-in 1 2),
> hence are not garbage and would (I guess) never get collected.  If
> some package spews out a lot of these overlays and fails to delete
> them during updates, as a result of narrowing, can that get a problem?

Of course it can be a problem.  Packages are expected to be careful with
such things and if necessary can use the recently mentioned `evaporate'
property to help garbage-collect them.  I think overlays should
default to the `evaporate' behavior, but it's probably too late to change
the default now.


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