def irc_downcase!(irc_string, casemapping = :rfc1459)
      case casemapping
      when :ascii
        irc_string.tr!(*@@ascii_map.reverse)
      when :rfc1459
        irc_string.tr!(*@@rfc1459_map.reverse)
      when :'strict-rfc1459'
        irc_string.tr!(*@@strict_rfc1459_map.reverse)
      else
        raise ArgumentError, "Unsupported casemapping #{casemapping}"
      end

      return irc_string
    end
def irc_downcase!(irc_string, casemapping = :rfc1459)
      case casemapping
      when :ascii
        irc_string.tr!(*@@ascii_map.reverse)
      when :rfc1459
        irc_string.tr!(*@@rfc1459_map.reverse)
      when :'strict-rfc1459'
        irc_string.tr!(*@@strict_rfc1459_map.reverse)
      else
        raise ArgumentError, "Unsupported casemapping #{casemapping}"
      end

      return irc_string
    end
Turn a string into IRC lower case, modifying it in place.
 @param [String] irc_string An IRC string (nickname, channel, etc)
 @param [Symbol] casemapping An IRC casemapping
 @return [String] A lower case version of the IRC string according to
   the casemapping