=begin
Suggestion: warn if the same character appears more than once in a character class (or more restrictedly: if the character ':' appears both at the start and end of a character class)
This is to give some indication of the problem if you do the following:
In message "Re: [ruby-core:24627] [Feature #1831] Suggestion: warn on repeated character in character class"
on Fri, 31 Jul 2009 08:01:30 +0900, Yui NARUSE redmine@ruby-lang.org writes: