> Even sillier question: how do you tell?

> Does that mean anything:
> [gus@gusmac libraries]$ hexdump -C redcloth.rb | head
> 00000000  23 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |#


[PLUG] I just open it in jEdit and look at the buffer properties :)

The dump show the first few characters (the hash mark followed by spaces
and the "vim..." macros) are ascii compliant (which doesn't mean much,
as utf-8 is also compliant for chars in these range).

Looking at your error, this is the PUNCT regexp plus the chars {(\[
which appear at line 459 of RedCloth.rb. (which duh I should have looked
at your original post...).
In the regexp's first line  there is a character class which contains a
parenthesis 
  (^|\s|\>|[#{PUNCT}{(\[])
IIUC, the opening parenthesis is a simple character when inside the
character, but you can try escaping it:
  (^|\s|\>|[#{PUNCT}{\(\[])

If that doesn't work, guess we'll wait till _why wakes up :-)