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

Joseph Wright joseph.wright at morningstar2.co.uk
Wed Dec 5 12:56:10 CET 2012

On 05/12/2012 08:54, Vafa Khalighi wrote:
>> 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{...}

I was thinking more at the level of something like \hboxR/\hboxL as
defined by bidi, plus perhaps some form of test similar to \ifmmode.
Then again, I have no idea what is needed beyond certain small contexts
(for example ensuring LTR for units).

>> 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.

Right, so some more thinking required here. The question is what is
sensible for new content: from what you say about TeX--XeT and bidi,
using pdfTeX/XeTeX is not currently to be recommended for RTL work
(although I guess this would change if XeTeX switches to the Omega
Joseph Wright

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