Trying to use the package
unicode-math I have been looking for some documentation of
\Umathcodenum, etc. The usually place, the package documentation (http://ctan.org/pkg/unicode-math), does not contain such. Unfortunately, I am not (yet) able to read LaTeX3 source code.
For example, by trial and error it seems that
\Umathcode`C="x"yy"zzzz is the right syntax of
\Umathcode. Of course, that is different from
\mathcode`C="xyzz (at least in the number of bits...).
So how is the syntax of