Re: Message Mode and bidi

[Eli Zaretskii <eliz@gnu.org>]

> From: Eric Abrahamsen <eric@ericabrahamsen.net>
> Date: Mon, 19 Feb 2024 16:46:22 -0800
> 
> Christopher Culver via "Emacs development discussions."
> <emacs-devel@gnu.org> writes:
> 
> > Joost Kremers <joostkremers@fastmail.fm> writes:
> >> When you compose a new message, is there a line "--text follows this line--"
> >> separating the headers and the message text? In my case, there is (I use mu4e)
> >> and when I type Arabic text on the line below this text, I get the effect you
> >> mention. If I leave an empty line after "--text follows this line--", bidi works
> >> as expected.
> >
> > Indeed, if I just go down one line and then begin typing, bidi works as
> > expected. I am feeling very foolish that I did not even try this. Thank
> > you for clearing up this problem, and for shedding light on how Emacs
> > considers paragraphs.
> 
> This is a bit weird, because the value of `mail-header-separator'
> ("--text follows this line--") is added to both `paragraph-start' and
> `paragraph-separate') in `message-mode'. You'd think one of those would
> do it.

Emacs doesn't use paragraph-separate and paragraph-start to define
where a paragraph starts and ends, for the purposes of determining the
base directionality of a paragraph.  It uses separate variables for
that, see the node "Bidirectional Editing" in the Emacs user manual.
The reason for using separate variables is because several modes,
including (but not limited to) message-mode, set the former variables
to regexps that get in the way of bidi reordering, and could easily
produce wrong results on display.