Re: Bidirectional editing in Emacs -- main design decisions

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 10 Oct 2009 23:13:48 +0800
> From: Jason Rumney <jasonr@gnu.org>
> CC: emacs-devel@gnu.org, emacs-bidi@gnu.org
> 
> Eli Zaretskii wrote:
> > 4. Reordering of text for display
> >   
> 
> Does the function font-shape-gstring help with fitting this in?

I'm sorry to say that I don't understand what it does.  If you can
explain, or give me an educational example to play with, maybe I will
be able to answer your question, my profound ignorance of GUI
rendering notwithstanding.

> > 8. User control of visual order
> >   
> >  I decided it was unjustified to deviate from UAX#9.  Its algorithm
> >  already provides the solution to this problem: users can always
> >  control the visual order by inserting special formatting codes at
> >  strategic places.
> 
> Couldn't Emacs by default use the clever heuristics to decide when to 
> automatically insert the special formatting codes? It would have to be 
> optional and undoable of course, because heuristics are never perfect, 
> but it seems to me as a naive non-speaker of RTL languages that to DWIM 
> in these edge cases is the right behaviour.

I agree: if it's possible to DWIM automatically, we should.  But you
are talking about higher levels than where I am right now.  For my
purposes, it was good enough to decide that any such clever heuristics
will eventually just add or remove formatting codes, and that no other
infrastructure features are needed to support this.

> Also you mention several times that the special direction change codes 
> are not displayed, but there should be an option to display them IMHO, 
> (perhaps part of whitespace.el) as users may need to distinguish between 
> explicit direction changes and implicit ones in some circumstances.

Yes, that's a very important feature, of course.  Which is why I
tried (but obviously failed, since you are the second person asking
the same) to tell that it will and must be supported:

   In addition, being able to show these formatting codes to the user
   is a valuable feature, because the way reordered text looks might
   not be otherwise understood or changed easily.