# File lib/mail/parsers/rfc2822_obsolete.rb, line 1402
    def _nt_obs_domain
      start_index = index
      if node_cache[:obs_domain].has_key?(index)
        cached = node_cache[:obs_domain][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0, s0 = index, []
      r1 = _nt_atom
      s0 << r1
      if r1
        s2, i2 = [], index
        loop do
          i3, s3 = index, []
          if has_terminal?(".", false, index)
            r4 = instantiate_node(SyntaxNode,input, index...(index + 1))
            @index += 1
          else
            terminal_parse_failure(".")
            r4 = nil
          end
          s3 << r4
          if r4
            r5 = _nt_atom
            s3 << r5
          end
          if s3.last
            r3 = instantiate_node(SyntaxNode,input, i3...index, s3)
            r3.extend(ObsDomain0)
          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(ObsDomain1)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:obs_domain][start_index] = r0

      r0
    end