# File lib/mail/parsers/rfc2822.rb, line 2566
    def _nt_mailbox_list
      start_index = index
      if node_cache[:mailbox_list].has_key?(index)
        cached = node_cache[:mailbox_list][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0 = index
      i1, s1 = index, []
      r2 = _nt_mailbox
      s1 << r2
      if r2
        s3, i3 = [], index
        loop do
          i4, s4 = index, []
          if has_terminal?(",", false, index)
            r5 = instantiate_node(SyntaxNode,input, index...(index + 1))
            @index += 1
          else
            terminal_parse_failure(",")
            r5 = nil
          end
          s4 << r5
          if r5
            r6 = _nt_mailbox
            s4 << r6
          end
          if s4.last
            r4 = instantiate_node(SyntaxNode,input, i4...index, s4)
            r4.extend(MailboxList0)
          else
            @index = i4
            r4 = nil
          end
          if r4
            s3 << r4
          else
            break
          end
        end
        r3 = instantiate_node(SyntaxNode,input, i3...index, s3)
        s1 << r3
      end
      if s1.last
        r1 = instantiate_node(SyntaxNode,input, i1...index, s1)
        r1.extend(MailboxList1)
      else
        @index = i1
        r1 = nil
      end
      if r1
        r0 = r1
      else
        r7 = _nt_obs_mbox_list
        if r7
          r0 = r7
        else
          @index = i0
          r0 = nil
        end
      end

      node_cache[:mailbox_list][start_index] = r0

      r0
    end