# File lib/treetop/compiler/metagrammar.rb, line 2213
      def _nt_optional_suffix
        start_index = index
        if node_cache[:optional_suffix].has_key?(index)
          cached = node_cache[:optional_suffix][index]
          if cached
            node_cache[:optional_suffix][index] = cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
            @index = cached.interval.end
          end
          return cached
        end

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

        node_cache[:optional_suffix][start_index] = r0

        r0
      end