# File lib/mail/parsers/rfc2822_obsolete.rb, line 2650
    def _nt_obs_id_left
      start_index = index
      if node_cache[:obs_id_left].has_key?(index)
        cached = node_cache[:obs_id_left][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      r0 = _nt_local_part

      node_cache[:obs_id_left][start_index] = r0

      r0
    end