# File lib/sinatra/respond_to.rb, line 192
      def charset(val=nil)
        fail "Content-Type must be set in order to specify a charset" if response['Content-Type'].nil?

        if response['Content-Type'] =~ /charset=[^;]+/
          response['Content-Type'].sub!(/charset=[^;]+/, (val == '' && '') || "charset=#{val}")
        else
          response['Content-Type'] += ";charset=#{val}"
        end unless val.nil?

        response['Content-Type'][/charset=([^;]+)/, 1]
      end