code: function BlockTxnPacket(response, witness) {
    if (!(this instanceof BlockTxnPacket))
      return new BlockTxnPacket(response, witness);
  
    Packet.call(this);
  
    this.response = response || new bip152.TXResponse();
    this.witness = witness || false;
  }
docs: Represents a `blocktxn` packet.
  @constructor
  @param {TXResponse?} response
  @param {Boolean?} witness
  @property {TXResponse} response
  @property {Boolean} witness