docs: function createProducer(tapVersion) {
    var producers = {
      '12': new TAP12Producer(),
      '13': new TAP13Producer()
    };
    var producer = producers[tapVersion];
  
    if (!producer) {
      throw new Error(
        'invalid or unsupported TAP version: ' + JSON.stringify(tapVersion)
      );
    }
  
    return producer;
  }