# File lib/mail/parsers/rfc2822_obsolete.rb, line 2733
    def _nt_obs_keywords
      start_index = index
      if node_cache[:obs_keywords].has_key?(index)
        cached = node_cache[:obs_keywords][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0, s0 = index, []
      if has_terminal?("Keywords", false, index)
        r1 = instantiate_node(SyntaxNode,input, index...(index + 8))
        @index += 8
      else
        terminal_parse_failure("Keywords")
        r1 = nil
      end
      s0 << r1
      if r1
        s2, i2 = [], index
        loop do
          r3 = _nt_WSP
          if r3
            s2 << r3
          else
            break
          end
        end
        r2 = instantiate_node(SyntaxNode,input, i2...index, s2)
        s0 << r2
        if r2
          if has_terminal?(":", false, index)
            r4 = instantiate_node(SyntaxNode,input, index...(index + 1))
            @index += 1
          else
            terminal_parse_failure(":")
            r4 = nil
          end
          s0 << r4
          if r4
            r5 = _nt_obs_phrase_list
            s0 << r5
            if r5
              r6 = _nt_CRLF
              s0 << r6
            end
          end
        end
      end
      if s0.last
        r0 = instantiate_node(SyntaxNode,input, i0...index, s0)
        r0.extend(ObsKeywords0)
      else
        @index = i0
        r0 = nil
      end

      node_cache[:obs_keywords][start_index] = r0

      r0
    end