On 01/03/2017 12:14, Jonathan Kew wrote:
> On 01/03/2017 11:59, Joseph Wright wrote:
>> Hello all,
>>
>> With example
>>
>> \font\OTtenrm="[lmroman10-regular.otf]/OT"
>> \OTtenrm
>> \TeXXeTstate=1
>> \beginR
>> abc
>> \endR
>> \bye
>>
>> the output is LTR with TL'16. Is this a known issue?
>
> Yes, this is expected behavior. The TeX--XeT direction controls (\beginR
> etc) control the ordering of words within a line, etc. (slightly more
> accurately, the direction in which nodes in an hlist progress), but do
> not override the inherent directionality of Unicode characters, so "abc"
> is still a sequence of three strong-LTR letters and they stay in their
> left-to-right order.
>
> (However, if you try
>
> \beginR
> abc def
> \endR
>
> I'd expect you to get output that reads "def abc" because the two words
> are ordered RTL, even though each of them remains LTR internally.)
>
> This is why it is possible -- for better or worse -- to do something like
>
> ...english text {\arabfont العربي} more english
>
> in a xetex document and have the isolated Arabic word appear with
> correct (internal) RTL directionality, without having to explicitly
> surround it with \beginR...\endR (although for a multi-word Arabic
> phrase that would be necessary); the RTL-ness of the characters controls
> their behavior within the word, despite the TeX direction remaining LTR.
>
> Currently, there isn't an option to make the TeX-level direction
> override the Unicode character directionality (comparable to the CSS
> property "unicode-bidi:bidi-override;"). Perhaps that would occasionally
> be useful, though people haven't exactly been clamouring for it AFAIK.
>
> JK
Thanks: all clear.
My guess is for the rare 'override' case one would probably do something
at the macro level in any case (kerning is all wrong to start with).
Joseph
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