[XeTeX] Math class initialization in Unicde-aware engine

[Joseph Wright]

On 28/11/2019 00:16, Ross Moore wrote:
> If by ignoring you mean removing the character entirely, then that is surely not best at all.
> 
> Most  N Class (Normal) characters would be simply of the default  \mathord  class.

That is already the case: it's where IniTeX starts off, chars are 
mathord. So 'nothing to do here'. Also note that some of this 
information is already set from the main Unicode file: it tells us which 
chars are letters.

> I’d expect others to be mapped instead into a macro that corresponds to something that TeX does support.
> e.g.
>   space characters for  thinspace, 2-em space, etc.  in  U+2000 – U+200A
> can expand into things like:   \, \; \> \quad \qquad  etc.  ( even to constructions like  \mskip1mu )

That's not a generic IniTeX thing, I'm afraid. The Unicode data loaders 
are explicitly about setting up the basic data in Unicode TeX engines 
that's held in (primitive) tables. Creating macros is the job of the 
'rest' of the format. Here, presumably you are thinking of making chars 
math-active: that's well out-of-scope for the loader.

> After all, this is essentially what happens when pdfTeX reads raw Unicode input.

pdfTeX reads bytes, there's not really much comparison. In IniTeX mode, 
there is not much happening with UTF-8 and pdfTeX: perhaps you are 
thinking of with LaTeX?

Joseph