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Re: bidi-display-reordering is now non-nil by default

From: Eli Zaretskii
Subject: Re: bidi-display-reordering is now non-nil by default
Date: Tue, 16 Aug 2011 09:47:17 +0300

> From: Chong Yidong <address@hidden>
> Cc: address@hidden, address@hidden, address@hidden
> Date: Mon, 15 Aug 2011 22:02:53 -0400
> Eli Zaretskii <address@hidden> writes:
> > More importantly, I don't think it's a good idea to change the bidi
> > properties in such a radical way (or at all), because we don't have
> > the resources to investigate all of the consequences.  For example, <
> > is a mirrored character, so when it's between to R2L characters, it
> > displays as > and vice versa.  Yes, I know: you'll suggest to change
> > the mirroring table as well, but how far should we go? do we really
> > want to create our own UBA?
> The specs allow for a "higher level protocol" to segment text according
> to what makes sense for (say) Lisp syntax, so anything that displays
> most realistic Lisp code correctly would be good enough.

"Higher level protocols" don't include futzing with bidirectional
properties of characters.  "Higher level protocol" means some means to
determine segment boundaries other than segment separator characters
that are part of the text.  Translated into Emacs-speak, this means we
need a variable that, when bound to some special value, instructs the
reordering engine to treat certain characters as segment separators.

> I guess this is not realistic to implement for 24.1

If we go with a variable described above, it's actually a very simple
job, so just say the word.  However, I suggest that before doing this
we come up with a more detailed plan: suppose you have this variable,
how would you solve the problems discussed here with its help?  The
devil is in the details.

> since there is no near-term solution, how bout turning off bidi
> display reordering for prog-mode buffers?

What for?  No one complained about it yet, and leaving it on helps
find bugs and inefficiencies in the bidi display engine.  So my vote
is NAY.

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