[XeTeX] Oldstyle figures in seperate file

[Andy Lin]

I think this topic has been discussed before, and at the time, there
was a suggestion of using the interchartoks mechanism, and so the
ucharclasses package might work for you. BUT, and I might be
remembering wrong, I think it was thought to be a bad idea to do this
with numbers.

But if you're feeling adventurous, you can try the below:

You can edit the ucharclasses sty file, and hijack one of the unicode
class entries (found at lines 696-877) to reflect the unicode range
you want (decimal 48-57), so let's say you have:
\newcommand{\@loadNumberForms}{\@defineUnicodeClass{\NumberFormsClass}{8528}{8591}}

You want to change this to:
\newcommand{\@loadNumberForms}{\@defineUnicodeClass{\NumberFormsClass}{48}{57}}

And then you put this in your preamble (I made up the font names):
\usepackage{fontspec}
\usepackage[NumberForms]{ucharclasses}
\setDefaultTransitions{\fontspec{Times New Roman}}{}
\setTransitionTo{NumberForms}{\fontspec{Times New Roman Expert}}

And... it should work. Or it might make xelatex very unhappy. One of the two.

Hope this helps,
Andy