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

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 31 Jul 2011 08:44:35 +0200 (CEST)
> Cc: emacs-devel@gnu.org
> From: Werner LEMBERG <wl@gnu.org>
> 
> > Emacs is searching for the beginning of the paragraph, but this
> > whole buffer is one huge paragraph.  The manual explains the
> > significance of the paragraph direction for the bidirectional
> > display, in case you are interested in the details.
> 
> Thanks.  Does a limit exist (say, 100kByte) as a maximum value for a
> paragraph length after that bidi-paragraph-direction is automatically
> set to right-to-left (if not overridden specifically) to circumvent
> this problem?

You mean left-to-right, not right-to-left, yes?  Setting the base
paragraph direction in that buffer to right-to-left will make the
display barely legible.

There's no such feature currently, no.  It could be easily added, but
I'm not sure such a heuristics is justified; it certainly can Do The
Wrong Thing in some cases, e.g., I could imagine a similar use case
with some mail summary buffer, but with the message numbers spelled in
Arabic digits and most of the Subject lines in Arabic or Farsi.  In
that case, the correct direction is actually right-to-left.  As
another example, I have a large text file with the entire Bible in
Hebrew, which is again one huge paragraph -- but its direction should
be right-to-left.

The design of determining the base paragraph direction dynamically as
part of redisplay is based on the assumption that most buffers either
have small enough paragraphs to not cause any significant slowdown, or
else are specialized buffers whose correct base direction is 100%
predictable in advance.  If you (or someone else) can see use cases
that break this assumption, please describe those use cases.