# File lib/mail/parsers/message_ids.rb, line 20
    def _nt_primary
      start_index = index
      if node_cache[:primary].has_key?(index)
        cached = node_cache[:primary][index]
        if cached
          cached = SyntaxNode.new(input, index...(index + 1)) if cached == true
          @index = cached.interval.end
        end
        return cached
      end

      r0 = _nt_message_ids
      r0.extend(Primary0)

      node_cache[:primary][start_index] = r0

      r0
    end