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Re: BIDI, LaTeX (auctex) and the «evil» backslash
From: |
Eli Zaretskii |
Subject: |
Re: BIDI, LaTeX (auctex) and the «evil» backslash |
Date: |
Sat, 21 May 2016 20:34:40 +0300 |
> From: Uwe Brauer <address@hidden>
> Date: Sat, 21 May 2016 13:55:18 +0000
> Cc: auctex-devel <address@hidden>
>
> In my understanding UTF distinguish between
What is "UTF" in this context?
> - LTR chars such as a,b,c
>
> - RLT chars such as א,ב,ג
>
> - «neutral» chars such as (),\ etc.
You should read the description of UBA, the Unicode Bidirectional
Algorithm (which Emacs implements). There you will see that there are
actually 4 classes of characters:
. string (LTR and RTL)
. weak (numbers, number separators, diacriticals)
. neutral (punctuation and whitespace)
. formatting control characters (RLM etc.)
So:
(get-char-code-property ?\\ 'bidi-class) => ON
("ON" stands for "other neutral", see the node "Character Properties"
in the ELisp manual.)
> - set bidi-paragraph-direction to left (shown in the next
> screenshot.) The display is correct, however typing Hebrew, when
> bidi-paragraph-direction is set to left is as unpleasant as
> writing English with bidi-paragraph-direction set to right.
>
> - use LRM chars before the backslash (see the last screenshot;
> having set `glyphless-char-display-control' to `acronym'.
> This looks well to but adding these chars is cumbersome.
>
> - hack auctex (CC to the auctex list): a new variable is
> introduced, say bidi-support, which is per default nil, but if it
> is t, then LRM chars are inserted before a backslash. I am
> pretty sure the auctex team will not like this idea very much.
>
> - back emacs: in a LaTeX buffer, backslash is considered as LTR, I
> don't know whether this can be done one the lisp level or whether
> it can be done at all.
>
> Comments?
The last one is possible, of course (this is Emacs), but that way lies
madness: arbitrarily changing bidirectional properties of characters
will bite you elsewhere, because the corresponding tables are global.
The other 3 alternatives are indeed the available solutions.
Personally, I recommend the 1st one; I see no problem with typing RTL
text in a left-to-right paragraph (and vice versa), and don't
understand what unpleasant things you bump into when doing that. TeX
files are fundamentally left-to-right, as any program text, so that
would be my suggestion.