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Re: Unexpected hiding of identical images


From: Stefan Monnier
Subject: Re: Unexpected hiding of identical images
Date: Mon, 18 Jul 2005 14:57:49 -0400
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

> And since the property list of the three images are fully identical
> (the same cons cell), the second and third images (intervals) which
> are adjacent to the first image (interval), are skipped by
> Fnext_property_change.

> I understand why the interval code does this for ordinary text
> properties, but it obviously breaks for the display property.

The problem is that text-properties are not really adapted for such uses.
After all, they apply to chars, not to text.  So by convention we consider
that contiguous properties that are `eq' make up a region/area/extent, which
works 99%.  For corner cases like yours, you have to work around the problem
by making sure your `cons' cells are not `eq'.

Another alternative is to use overlays.  Except that overlays are not
duplicable and don't apply to strings.  That's where XEmacs's extents
make sense.


        Stefan




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