Re: [emacs-bidi] Hebrew characters categories

[Yair Friedman (Jerusalem)]

TAKAHASHI Naoto <address@hidden> writes:

> Composition is independent of categories.  You can compose characters
> without using categories at all.  Never mind those categories designed
> for Thai and Lao; they were defined because they help composition in
> those languages.  You do not have to use them for Hebrew.

Yes, but they *do* help in composition for Hebrew as well (this is why I
chose them in the first place).  In addition, the phonetic categories
helps in resolving placement collision.

Do you think there is a better approach?  I'm sorry, but I don't know
enough about Emacs internals to start a whole new design.  The Thai
solution did seem like a good place to start.

>> If Emacs will continue with the mixed approach, then we would need 13
>> categories for Hebrew, most of them new.
>
> Create any categories if you think they are necessary for Hebrew.  Do
> not create any categories if you can do without them.
>

I don't want to create categories if it can be avoided, I'm asking for
your advise on what is the way to go. I think the separation of phonetic
and typographic categories is a good thing.

>> What is the approach taken in Arabic?
>
> For positioning, no new categories are defined.  Since Arabic vowel
> signs and other marks are aligned to centre, all we have to worry is
> whether they are placed above the base character or below.  Such
> vertical positioning is automatically done by the display engine,
> based on the glyph information stored in the font file.

So do you force the vowel sign to same vertical position always? Even
in cases such as Bah Vs Tah with Fatha and possibly Shadda? What about
Alif?  Do you use special presentation forms or somehow adjust the
composition.  Do you have assumptions about the font structure?