[XeTeX] Why is the fraction off the math axis in XeTeX?

[Ulrike Fischer]

Am Sun, 6 Dec 2015 15:00:42 +0100 schrieb Henri Menke:

> The fraction in textstyle is off the math axis in XeTeX when I use a
> Unicode math font.
> $-{1\over 2}$

> How can I fix this? Does it suffice to adjust \fontdimen parameters?

Imho it is an engine bug in the implementation of \over. The math
combines a textstyle minus with a scriptstyle subformula (1\over 2).
This involves two font sizes and so two different sets of \fontdimen
values, and xetex seems to use the axis fontdimen from the wrong
font (the smaller from the subformula).

It doesn't look as if one can change the \fontdimen when unicode
math fonts are used  -- and it wouldn't solve the problem: the
\fontdimen are not wrong, they are used wrongly. 


-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/