[luatex] \predisplaydirection from etex in luatex has no effect

Vafa Khalighi vafakh84 at gmail.com
Thu Apr 8 11:23:08 CEST 2010

> This stuff is trickier then one would expect, because of interactions
> between \mathdir, \pardir, and \leqno / \eqno.


> The big question is this: should \eqno and \leqno adhere to \pardir,
> to \mathdir, or simply be physical right and left without regard to
> direction specifiers at all? I don't know the answer to that, so
> somebody has to enlighten me.
I am just saying this as my own perspective and it does not need to be
correct. Firsty several diferent scripts use RTL writing and the convention
for writing maths is different from one RTL script to the other. As an
example Persian maths is exactly like LTR maths, we do not do RTL maths
\eqno should appear on RHS and \leqno should appear on LHS. but I think in
Arabic, they have RTL maths as well, and so the place of \eqno and \leqno is
interchanged. In other RTL scripts, they do maths LTR, but the place of
\eqno and \leqno is interchanged.

So from my perspective, \eqno, \leqno should not be changed at all if say
the user just says, \pagedir TRT \pardir TRT \bodydir TRT \textdir TRT or
\pardir TRT \textdir TRT, but it makes sense that when you have \mathdir
TRT, the place of \eqno and \leqno is interchanged (This whole paragraph is
the default behaviour of luatex now which is correct)

Best wishes,
Vafa Khalighi
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