[XeTeX] fontspec v1.7

[Will Robertson]

Ross Moore wrote:
> how shall we proceed to implement mathematics
> properly ?
> 
> Indeed, what does *properly* actually mean now ?

I would suggest that *properly* means that a unicode maths font can be 
set up in XeTeX to typeset maths in a maths environment, up to the level 
of writing in the literal glyphs if that is desired (but control 
sequences in general would be easier).

There are many problems with this, the biggest, as I see it, being that 
TeX needs all those extra font dimensions that unicode fonts simply 
lack, as far as I am aware. But if I recall correctly, Michael Downes 
wrote a package that dealt with maths doing all of the spacing 
explicitly, so it's at least possible in theory. (breqn?)

But this is a further reaching goal. The problem started with fontspec 
doing bad things with maths, and this is something that needs to be fixed.

First: do we actually want \mathrm to take the font of the text?

If so, then we simply need to remove the Knuthian assumptions that the 
maths font can take various accents and analphabetics from the text font 
and replace those definitions with fixed references to glyphs in a 
similarly old-fashioned font. So, if no other maths fonts are loaded, 
then the maths accents should be defined in terms of Computer Modern, 
and probably similarly with euler. lucbmath I haven't yet looked through 
but I'm sure that situation's similar.

Do we agree so far? For now, maths is strictly legacy, and the maths 
font packages need to be patched in XeLaTeX to reflect this. Beyond this 
I really don't know enough of the details to comment, yet...

Will