From xemacs-m  Thu Jan  2 04:58:02 1997
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Subject: bug in (at least) 19.14 to beta 6 in atomic extents 
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From: Jens Lautenbacher <jens@lemcbed.lem.uni-karlsruhe.de>
Date: 02 Jan 1997 11:59:47 +0100
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consider the following buffer:

-------------------------------------------
:start:
ksdjflklkjlk
sdfsdfkhkjhs
slkdjlkjlkjk
:stop:


(progn
  (load-library "atomic-extents")
  (set-extent-property
   (make-extent
    (save-excursion
      (goto-char (point-min))
      (search-forward ":start:"))
    (save-excursion
      (goto-char (point-min))
      (- (search-forward ":stop:") 6)))
   'atomic t))
-------------------------------------------

As you sure can see, eval'ing the progn results in the text between
:start: and :stop: being made atomic.

Setting the cursor at the end of the :stop: and moving backwards
demonstrates this nicely: You get to the first ':' from :stop: and
with the next backward-char to the first ':' from :start:

The bug is demostrated in the following:
Moving the cursor to the beginning of the line under :stop: and moving
up. The cursor hangs at the first ':' from :stop:. You need an
additional backward-char to get over the atomic extent. I consider
this a bug _not_ a feature! While one will be able to recover from the
above situation easily by the visual fdeedback this will be more
frustrating if also 'invisible is set.

Unfortunately this is just one of the extent squirks. Per Abrahamsen
had some bad luck with them also during implementing his new custom
library. 

