Re: [emacs-bidi] Unicode Bidi

[Eli Zaretskii]

> From: Roozbeh Pournader <address@hidden>
> Date: Sat, 20 Jan 2001 19:22:01 +0330 (IRT)
> 
> I was just reading the UTR9 and found that it agrees with my definition of
> "logical". Section "3.12" tells:
> 
>       The Unicode Standard prescribes a /memory/ representation order
>       known as logical order.
> 
> and later,
> 
>       This allows exact control of the display ordering for legible
>       interchange and also ensures that plain text used for simple items
>       like filenames or labels can always be correctly ordered for
>       display.
> 
> So it has to do nothing with the typing order, it's all about
> interchangablity of text.

I think you are misinterpreting UTR9.  According to my understanding,
all this says is that Unicode requires that characters be layed out in
memory in the logical order.  But it doesn't define what the logical
order is, at least not in the quotations you show above.

The reason it talks about ``exact control of the display ordering'' is
that visual order makes it much harder to ensure correct display when
display dimensions change, for example if you say "C-x 3" in Emacs,
which divides the current window into two windows, with lines half the
previous size.  If the word processor supports automatic line wrapping
(auto-fill in Emacs parlance) which refills when the line width
changes (Emacs doesn't do that currently), and if the new right margin
happens to be in the middle of a L2R text embedded it an otherwise R2L
paragraph, visual order doesn't allow to refill the text easily, while
logical order does.

Similar things happen with file names that mix L2R and R2L characters
(another case that Word gets wrong, btw).