# File lib/mail/parsers/rfc2822.rb, line 648
    def _nt_comment
      start_index = index
      if node_cache[:comment].has_key?(index)
        cached = node_cache[:comment][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0, s0 = index, []
      if has_terminal?("(", false, index)
        r1 = instantiate_node(SyntaxNode,input, index...(index + 1))
        @index += 1
      else
        terminal_parse_failure("(")
        r1 = nil
      end
      s0 << r1
      if r1
        s2, i2 = [], index
        loop do
          i3, s3 = index, []
          r5 = _nt_FWS
          if r5
            r4 = r5
          else
            r4 = instantiate_node(SyntaxNode,input, index...index)
          end
          s3 << r4
          if r4
            r6 = _nt_ccontent
            s3 << r6
          end
          if s3.last
            r3 = instantiate_node(SyntaxNode,input, i3...index, s3)
            r3.extend(Comment0)
          else
            @index = i3
            r3 = nil
          end
          if r3
            s2 << r3
          else
            break
          end
        end
        r2 = instantiate_node(SyntaxNode,input, i2...index, s2)
        s0 << r2
        if r2
          r8 = _nt_FWS
          if r8
            r7 = r8
          else
            r7 = instantiate_node(SyntaxNode,input, index...index)
          end
          s0 << r7
          if r7
            if has_terminal?(")", false, index)
              r9 = instantiate_node(SyntaxNode,input, index...(index + 1))
              @index += 1
            else
              terminal_parse_failure(")")
              r9 = nil
            end
            s0 << r9
          end
        end
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(Comment1)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:comment][start_index] = r0

      r0
    end