# File lib/mail/parsers/content_transfer_encoding.rb, line 68
    def _nt_encoding
      start_index = index
      if node_cache[:encoding].has_key?(index)
        cached = node_cache[:encoding][index]
        @index = cached.interval.end if cached
        return cached
      end

      i0 = index
      r1 = _nt_known_tokens
      if r1
        r0 = r1
      else
        r2 = _nt_ietf_token
        if r2
          r0 = r2
        else
          r3 = _nt_x_token
          r3.extend(Encoding0)
          if r3
            r0 = r3
          else
            @index = i0
            r0 = nil
          end
        end
      end

      node_cache[:encoding][start_index] = r0

      r0
    end