Re: Bidirectional text and URLs

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 30 Nov 2014 04:38:04 -0500
> From: Richard Stallman <rms@gnu.org>
> CC: schwab@linux-m68k.org, larsi@gnus.org, emacs-devel@gnu.org
> 
>  > > This suggests we need to provide a primitive to tell Lisp programs a
>   > > guaranteed answer for which direction the text at a certain point is
>   > > displayed in.
> 
>   > The directionality of the text is determined by the display engine,
>   > and by design is not subject to control by Lisp programs,
> 
> I think we are talking about different issues.  You're talking about
> whether Lisp programs control the directionality.  I'm talking about
> providing a way for them to inquire what display will do.

I apologize for my misunderstanding.

>   > > Also, a primitive to verify that a certain region of text has no
>   > > bidi strangeness within it.
> 
>   > We need to have a good instrumental definition of "bidi strangeness"
>   > for that.
> 
> I suggest the definition: whatever would cause the displayed order of
> characters to be perhaps misleading if the text is interpreted as a
> URL or anything else with programatic significance.

I'm sorry, but this is not instrumental: it doesn't specify what
"misleading" means.  We need a detailed spec for that.  The underlying
problem here is that many cases of what readers of RTL scripts will
perceive as perfectly valid reordering might appear "misleading" to
people who don't read those scripts.  We should strive to arrive at a
definition that detects unreasonable and suspicious reordering, not
just any reordering.

One possible definitions for "misleading" were suggested earlier:
strict left-to-right text which is reordered for display due to
directional control characters.  If this is what we want, I can work
on providing infrastructure for detecting these cases (and perhaps
also similar ones for when similar games are played with URLs that use
RTL characters).

If that is not what we want, then we need to continue discussing the
requirements.