code: @Override
    public List<Record> signalStartTrack(Record signal) {
      //(queue track)
      this.queuedTracks.addLast(signal);
      //(push info)
      if(info != null){
        this.trackStack.push(info);
      }
      info = new TrackInfo(signal.content.toString(), signal.timesstamp);
      //(force print)
      if(signal.force()){
        updateTracks(signal.depth+1);
      }
      //(return)
      return EMPTY; //don't send extra records
    }
docs: {@inheritDoc}