[antlr-interest] Examining characters in lexer

[Dennis Brothers]

Is there a special symbol or method that returns the character about  
to be scanned?  In order to handle a variety of (natural) languages,  
I'd like to use Unicode categories to detect various character types  
(particularly letters).

I want to do something like

fragment LETTER : { Char.IsLetter( $char ) } ?=> . ;

where $char is the next character to be scanned and Char.IsLetter() is  
a .NET method that examines a character's Unicode category and returns  
true if it's one of the letter categories.

While I'm at it, is it legal to use a gated predicate like the above  
in a lexer?

Thanks -
     - Dennis Brothers