[luatex] Info on direction primitives/implementation

[Joseph Wright]

On 04/12/2012 12:58, Taco Hoekwater wrote:
> There is (of course) much more detail than this, but that is the overview.

Two follow-on questions :-)

First, I see that there are five primitives doing the work here:
\textdir, \mathdir, \pardir, \bodydir and \pagedir. The first two are
easy enough to understand, and I think I get \pardir (flips where the
\indent and so forth are). However, I'm not really clear on \bodydir and
\pagedir: anyone got a good explanation?

Secondly, I'm a bit unsure about the detail on \mathdir when it comes to
numerals. From what I understand, numbers read in decreasing magnitude
left-to-right in both LTR and RTL languages, so for example pi is always

   3.1415...

and never

  ...5141.3

even when using (real) Arabic numerals rather than the 'arabic' ones of
the European tradition. However, \mathdir flips everything: is that
correct, and if so is the expectation that numerals in math mode are
handled using a Lua callback?
-- 
Joseph Wright