Hi David,
On 06/11/2013, at 8:07 AM, David Carlisle wrote:
> On 05/11/2013 20:34, Ross Moore wrote:
>> Directionality is a property of the math environment, not of the
>> content in that environment
>
>
> Usually but not always. After the review of use cases in the Arabic math
> note, directionality in MathML3 is allowed at the level of <mrow>, not
> just on the top level <math>. (Whether any particular TeX or MathML
> rendering agent can support switching at that level is another issue but
> the specification allows it.)
OK. Thanks for that clarification.
On 06/11/2013, at 8:43 AM, Khaled Hosny wrote:
> On Wed, Nov 06, 2013 at 07:34:05AM +1100, Ross Moore wrote:
>> I would vote for inserting something like \mathdir{rtl}
>
> Please note that \mathdir is already an Omega/Aleph/LuaTeX[1] primitive
> name.
>
> Regards,
> Khaled
>
> 1. In case of LuaTeX it is "hidden" by default, but formats my choose to
> enable it.
With this information, my advice would be to have a macro that
effectively just sets a switch, in the usual TeX-like way,
whose value is confined to a brace-delimited environment.
Internal macro expansion either respects the value of that switch
or ignores it.
The details are left to developers to fill in.
e.g. user-syntax could be:
\[
x^2 + 2\,x + 1 =
\begin{cases}
(x+1)^2 & \text{ in Roman LTR script (LTR)}\\
{\setmathdir{rtl} (x+1)^2 } & \text{in Arabic (RTL)}
\end{cases}
\]
Thus in Omega/Aleph/LuaTeX the primitive is set locally.
Other formats would need to implement much more to get it right,
or just gobble the argument and issue a warning message that
directionality support is not yet available.
This is in accordance, I think, with the discussion here:
http://tug.org/pipermail/luatex/2012-December/003929.html
where direct use of the primitive is delimited.
>
> David
Hope this helps,
Ross
------------------------------------------------------------------------
Ross Moore ross.moore@mq.edu.au
Mathematics Department office: E7A-206
Macquarie University tel: +61 (0)2 9850 8955
Sydney, Australia 2109 fax: +61 (0)2 9850 8114
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