[racket] Unicode regexp character classes?

Are there any unicode regular expression character classes?

I'm hoping for something similar to [:alpha:], etc. that are based 
around, say, the first letter of the unicode character classification.  
I *can* do what I want by disassembling strings by hand and using tests 
based on char-general-category, but a regular expression would (should?) 
be much neater.

(I know that these aren't mentioned in the documentation, but it just 
says that it's talking about the "Frequently Used Character Classes", 
not that there aren't any others.)

-- 
Charles Hixson