You may wish to visit, for example, the egrep(1) man page for a 
description of regular expressions.  Note that the [a-zA-Z] and [aA-zZ] 
regular expressions are different.  The former contains the alphabetic 
characters.  The latter is equivalent to [A-z], which in ASCII also 
contains several other characters between 'A' and 'z', including '_'.

Jason

Eliot Handelman wrote:
> This doesn't seem right:
> 
> 
>        Objective Caml version 3.08.0
> open Str
> 
> let search r str =
>  search_forward (regexp r) str 0;
>  matched_string str;;
> 
> # search "[aA-zZ]+" "_test";;
> - : string = "_test"
> 
> whereas:
> 
> # search "[a-zA-Z]+" "_test";;
> - : string = "test"
> 
> 
> -- eliot
> 
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-- 
Jason Hickey                  http://www.cs.caltech.edu/~jyh
Caltech Computer Science      Tel: 626-395-6568 FAX: 626-792-4257