[XeTeX] \beginR ...\endR

Jonathan Kew jonathan_kew at sil.org
Thu Nov 4 21:09:04 CET 2004

On 4 Nov 2004, at 7:11 pm, Michael Gedalin wrote:

> I am typesetting the following:
> \documentclass{article}
> \TeXXeTstate=1
> \begin{document}
> \beginR
> first
> \endR
> \beginR
> second
> \endR
> \beginR
> third
> \endR
> \end{document}
> and get
> "tsfri"  (flushed left)
> "dnoces" (flushed right)
> "third" (flushed left)
> log complains about
> \endL or \endR problem (0 missing, 1 extra) for the second and third.
> Is this normal or am I doing something wrong ?
> Michael

There should be documentation on the TeX--XeT direction primitives 
somewhere among the e-TeX documentation, as this is a standard e-TeX 
feature. But to address your example in brief:

The \beginR...\endR (or L) commands need to be properly balanced 
*within* each paragraph, with the exception that you omit the final 
\endR if the paragraph is to be right-to-left overall. So to explain 
your results:

(1) is flush left because the actual paragraph end doesn't happen until 
after the \endR. If you remove that, it'll be flush right instead (with 
no complaints).

(2) is flush right because the paragraph ends in R mode, but then 
complains because of the \endR *after* the paragraph has ended. Again, 
you simply don't want that at all.

(3) is flush left because the \beginR is actually in a paragraph all by 
itself (because of the following blank line), so there's no \beginR 
within the paragraph, just an \endR (which generates the complaint).

If you're wanting to set a series of right-to-left paragraphs, you need 
to begin each one with \beginR, and don't use any \endR. \everypar is a 
handy way to do this. A common incantation is something like:

	\everypar={\setbox0=\lastbox \beginR \box0 }

before a series of paragraphs. (The box manipulation is to deal with 
the paragraph indent, which has already been generated before \everypar 
is expanded; we need to move it so that it occurs after the \beginR.)

> PS On the same occasion: why not \TeXXeTstate=1 by default ? Does it 
> interfere with anything ?

According to the e-TeX code, the additional nodes that it inserts into 
TeX's internal lists can potentially have an effect on line-breaking or 
hyphenation; I forget the precise details. So it's possible, in obscure 
cases, that the layout of a purely unidirectional standard TeX document 
could be affected by enabling the feature. But unless you require 
absolute document stability when moving documents between TeX and 
e-TeX, it probably doesn't matter to you.



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