[XeTeX] Unicode Properties

[Bruno Le Floch]

Hello,

I would like to know if it is possible to access the Unicode
properties of a given character from within XeTeX (e.g., "Upper case
letter", or "Surrogate character").

I am thinking of this in the context of a recent experimental addition
to LaTeX3 of a regular expression engine. Currently, it supports
Unicode characters, but only very superficially because I haven't put
Unicode property support, among other things.

Regards,
Bruno