# File lib/mail/parsers/rfc2822.rb, line 4743
    def _nt_id_left
      start_index = index
      if node_cache[:id_left].has_key?(index)
        cached = node_cache[:id_left][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0 = index
      r1 = _nt_message_id_text
      if r1
        r0 = r1
      else
        r2 = _nt_no_fold_quote
        if r2
          r0 = r2
        else
          r3 = _nt_obs_id_left
          if r3
            r0 = r3
          else
            @index = i0
            r0 = nil
          end
        end
      end

      node_cache[:id_left][start_index] = r0

      r0
    end