[luatex] The effect of \pardir and \textdir on \indent and \parfillskip
Joseph Wright
joseph.wright at morningstar2.co.uk
Wed Dec 12 10:12:23 CET 2012
On 12/12/2012 09:03, Joseph Wright wrote:
> Hello all,
>
> Continuing my attempts to understand RTL primitives in LuaTeX, I've come
> across what I'd regard as unexpected behaviour in terms of the
> relationship between \textdir and \pardir.
>
> For example, in the demo
>
> \newbox\mybox
> \parskip 1 em %
>
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
>
> \pardir TRT
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
>
> \leavevmode
> \setbox\mybox=\lastbox
> \textdir TRT\box\mybox\textdir TLT
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
> Hello world Hello world Hello world Hello world Hello world
>
> \bye
>
> I find it surprising that the middle paragraph has the \indent on the
> left, and that it's necessary to alter the text direction to get it on
> the right.
>
> How do others see this: is the current behaviour 'expected', and more
> importantly is it useful? (OK, most of the time \pardir and \textdir
> will agree on direction, but my reading of the primitive names was that
> they are intended to separate out the run of the text and the shape of
> the paragraph.)
BTW, I assume the argument for the behaviour is something like 'the
\indent is just an \hbox, so it's treated like any other, while the
\parfillskip is not a box, so is attached to the end of the paragraph in
a different way'.
--
Joseph Wright
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