[luatex] The effect of \pardir and \textdir on \indent and \parfillskip

[Joseph Wright]

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