Emacs & Hebrew

[Omer Zak]

On Wed, 2012-06-13 at 19:15 +0300, Eli Zaretskii wrote:
> > From: w1 at zak.co.il (Omer Zak)
> > It is a question of control.
> 
> If you use Emacs, you know that giving the user control is one of
> Emacs's main design principles.

Great!

> > So when one wants to view BiDi text in visual order (the usual case),
> > one opens the file in Gedit.  And when one wants to see it in logical
> > order (e.g. to figure out how the visual order turned out to be so
> > messed up), one opened it in Emacs.
> 
> Suppose the visual order is never "messed up" in Emacs -- do you still
> need this switch?

YES.  The Unicode BiDi algorithm is not perfect and it sometimes messes
up the visual order of BiDi strings.  The BiDi algorithm implementation
in Emacs must follow the Unicode standard.  Hence, it is inevitable that
there'll be some cases, in which the visual order is messed up in Emacs.
In fact, not to be messed up in those pathological cases would actually
be a bug in Emacs' BiDi algorithm implementation.

> > Another use case is by blind computer users, who prefer to use Braille.
> > All BiDi Braille text must be laid out in logical order.  So even if
> > your editor supports Hebrew Braille fonts, they are of no use if the
> > text is - too helpfully - printed out in visual order.
> 
> I don't know enough about this, but isn't Hebrew Braille just an
> encoding of Hebrew letters using Braille characters?  If so, then
> Braille characters all have string left-to-right directionality, and
> therefore will not be reordered for display by Emacs.

No.  The same standard encoding is used.  Braille is just another font.
To do otherwise would render regular Hebrew text inaccessible to the
Hebrew speaking blind computer users.
This font, however, needs to be rendered by bypassing the BiDi
algorithm.

> But even if the above does not solve the issue, I would expect people
> to request that Emacs does TRT by default with Hebrew Braille, rather
> than turning bidi off.

What does TRT stand for?

Turning BiDi off would be a satisfactory solution in this use case.  I
envision that sometime in the future, an Emacs startup script be
devised, such that swithcing to Hebrew Braille font would by default
switch BiDi off.

> 
> > Few years ago, when Abiword people were debugging BiDi support, I asked
> > for an option to turn it off for the benefit of blind Hebrew computer
> > users.  This request was turned down.
> 
> Well, I hope you agree now that Emacs is not Abiword...

:-)

--- Omer


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