XeTeX 1.0 wishlist: \fontdimen's

Hi Jonathan,

This is just a small issue, really, but if you're chasing down little  
things for a 1.0 release then perhaps it qualifies.

We've spoken before, I think, about how XeTeX isn't very good a  
filling in \fontdimen values for non-tfm fonts. I also know that in  
many cases they're not even relevant for fonts that are loaded. But  
having them would be nice, and they can be ignored in non-Latin font.

I'm especially interested in two: \fontdimen1 and \fontdimen5, slant  
and ex-height. (I'm quite happy with \fontdimen6 = point size.) For  
the first, this information might not be available to you, but not  
setting it breaks LaTeX's ability to nest \emph{}s; I'll be including  
a fix for this in the next version of fontspec, but I can see it  
being useful in other circumstances also.

If you can't get that info from a font, can it be set to a fixed  
positive value if you know the font is italic?

For the ex-height of a font, this is closely linked with not knowing  
the height of the boxes passed to XeTeX. I'm not asking for the  
latter (although I reiterate it'd be nice to have via a character  
height-measuring primitive), but measuring the height of an "x" (or  
maybe a different character, or maybe an average of a few) when the  
font is loaded would be quite useful, in my opinion.

Thanks for your hard work!

Will