    # File lib/action_mailer/vendor/text-format-0.6.3/text/format.rb, line 335
        def hyphenator=(h)
          raise ArgumentError, "#{h.inspect} is not a valid hyphenator." unless h.respond_to?(:hyphenate_to)
          arity = h.method(:hyphenate_to).arity
          raise ArgumentError, "#{h.inspect} must have exactly two or three arguments." unless [2, 3].include?(arity)
          @hyphenator = h
          @hyphenator_arity = arity
        end