# File lib/treetop/compiler/metagrammar.rb, line 1773
      def _nt_optional_suffix
        start_index = index
        if node_cache[:optional_suffix].has_key?(index)
          cached = node_cache[:optional_suffix][index]
          if cached
            cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
            @index = cached.interval.end
          end
          return cached
        end

        if has_terminal?('?', false, index)
          r0 = instantiate_node(Optional,input, index...(index + 1))
          @index += 1
        else
          terminal_parse_failure('?')
          r0 = nil
        end

        node_cache[:optional_suffix][start_index] = r0

        r0
      end