code: function TXPacket(tx, witness) {
    if (!(this instanceof TXPacket))
      return new TXPacket(tx, witness);
  
    Packet.call(this);
  
    this.tx = tx || new TX();
    this.witness = witness || false;
  }
docs: Represents a `tx` packet.
  @constructor
  @param {TX|null} tx
  @param {Boolean?} witness
  @property {TX} block
  @property {Boolean} witness