bug#21848: Bug in emacs: filling a certain region with (fill-region) causes a certain character to disapear

[Ruy Exel]

Hi Glenn,

Thanks for your reply.  The great thing abour Emacs is that, even if
you've been using it almost daily for the past 25 years, there is
always a lot to learn!

Best,
Ruy

On Sat, Nov 7, 2015 at 3:20 AM, Glenn Morris <rgm@gnu.org> wrote:
> Ruy Exel wrote:
>
>> 2) Mark a region consisting of the first two lines, namely
>>
>> | a |
>> | a
>>
>> 3) Observe that these two lines contain *three* vertical bars
>> 4) Run the command "ESC-x fill-region"
>> 5) Observe that thare are only *two* vertical bars now!
>
>
> This is not a bug, but rather "adaptive filling" behaving as designed.
> Compare the result if you first: (setq adaptive-fill-mode nil).