[XeTeX] [luatex] Info on direction primitives/implementation

[Vafa Khalighi]

>
> At the moment, I'm looking specifically at what we need to worry about
> at a low level. For example, the current expl3 code does not take any
> notice of direction, which is probably right for something like \hbox:n
> (follow whatever is going on around it), but should be documented and
> deliberate, not just something we've ignored. So what's important at
> this stage is much more the concepts than trying to write any code,
> although any thoughts on what is required for RTL support at the 'base
> level' are of course welcome.
 

For the boxes in luatex you can change directions: \hbox dir TRT{...}

>
>
> What you say fits in with what I'd already suspected: for RTL work,
> we've be better only supporting one set of primitives, the Omega ones.
 
Yes, because if you want to typeset TeX--XeT, you will find that you have to patch a lot due to the limitaions/bugs of the engine which is wrong.

>
> For pdfTeX that's not an issue: I doubt very many people use pdfTeX for
> RTL. 
 
Well, there are two groups of people. The first group use ArabTeX which does not make any use of TeX--XeT and it works with Knuth TeX too. The second group also are Hebrew and Arab users; some of them still use babel.
> XeTeX is a bit more 'interesting': I guess the existence of bidi
> means that people are using XeTeX for 'real life' RTL work, despite
> limitations.
 

Considering bidi has improved the situations and made things cleaner and simpler, yes.
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