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Re: Info mutilates user overlays.

From: Luc Teirlinck
Subject: Re: Info mutilates user overlays.
Date: Wed, 1 Oct 2003 09:49:11 -0500 (CDT)

Stefan Monnier wrote:

   You say this is unexpected, but you don't say what you expected.
   The text of the buffer has changed, so the overlay has of course been
   moved, as is always the case.

On second thought yes.  Also, there are worse problems in Info than
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
he has saved, say 10 bookmarks, but all but the last are gone and it
is saved under a misleading name.  Position registers and bookmarks are
mainly useful in large files, so the one place where they would be the
most useful (if they worked) are Info files.

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.

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?



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