# File lib/mail/parsers/content_transfer_encoding.rb, line 101
    def _nt_known_tokens
      start_index = index
      if node_cache[:known_tokens].has_key?(index)
        cached = node_cache[:known_tokens][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0 = index
      if has_terminal?("7bit", false, index)
        r1 = instantiate_node(SyntaxNode,input, index...(index + 4))
        @index += 4
      else
        terminal_parse_failure("7bit")
        r1 = nil
      end
      if r1
        r0 = r1
      else
        if has_terminal?("8bit", false, index)
          r2 = instantiate_node(SyntaxNode,input, index...(index + 4))
          @index += 4
        else
          terminal_parse_failure("8bit")
          r2 = nil
        end
        if r2
          r0 = r2
        else
          if has_terminal?("binary", false, index)
            r3 = instantiate_node(SyntaxNode,input, index...(index + 6))
            @index += 6
          else
            terminal_parse_failure("binary")
            r3 = nil
          end
          if r3
            r0 = r3
          else
            if has_terminal?("quoted-printable", false, index)
              r4 = instantiate_node(SyntaxNode,input, index...(index + 16))
              @index += 16
            else
              terminal_parse_failure("quoted-printable")
              r4 = nil
            end
            if r4
              r0 = r4
            else
              if has_terminal?("base64", false, index)
                r5 = instantiate_node(SyntaxNode,input, index...(index + 6))
                @index += 6
              else
                terminal_parse_failure("base64")
                r5 = nil
              end
              if r5
                r0 = r5
              else
                @index = i0
                r0 = nil
              end
            end
          end
        end
      end

      node_cache[:known_tokens][start_index] = r0

      r0
    end