# File lib/mail/parsers/rfc2822.rb, line 4567
    def _nt_message_ids
      start_index = index
      if node_cache[:message_ids].has_key?(index)
        cached = node_cache[:message_ids][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0, s0 = index, []
      r1 = _nt_msg_id
      s0 << r1
      if r1
        s2, i2 = [], index
        loop do
          i3, s3 = index, []
          r4 = _nt_CFWS
          s3 << r4
          if r4
            r5 = _nt_msg_id
            s3 << r5
          end
          if s3.last
            r3 = instantiate_node(SyntaxNode,input, i3...index, s3)
            r3.extend(MessageIds0)
          else
            @index = i3
            r3 = nil
          end
          if r3
            s2 << r3
          else
            break
          end
        end
        r2 = instantiate_node(SyntaxNode,input, i2...index, s2)
        s0 << r2
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(MessageIds1)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:message_ids][start_index] = r0

      r0
    end