# File lib/mail/parsers/rfc2822_obsolete.rb, line 490
    def _nt_obs_day_of_week
      start_index = index
      if node_cache[:obs_day_of_week].has_key?(index)
        cached = node_cache[:obs_day_of_week][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      i0, s0 = index, []
      r2 = _nt_CFWS
      if r2
        r1 = r2
      else
        r1 = instantiate_node(SyntaxNode,input, index...index)
      end
      s0 << r1
      if r1
        r3 = _nt_day_name
        s0 << r3
        if r3
          r5 = _nt_CFWS
          if r5
            r4 = r5
          else
            r4 = instantiate_node(SyntaxNode,input, index...index)
          end
          s0 << r4
        end
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(ObsDayOfWeek0)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:obs_day_of_week][start_index] = r0

      r0
    end