code: function MTX(options) {
    if (!(this instanceof MTX))
      return new MTX(options);
  
    TX.call(this);
  
    this.mutable = true;
    this.changeIndex = -1;
    this.view = new CoinView();
  
    if (options)
      this.fromOptions(options);
  }
docs: A mutable transaction object.
  @alias module:primitives.MTX
  @extends TX
  @constructor
  @param {Object} options
  @param {Number?} options.version
  @param {Number?} options.changeIndex
  @param {Input[]?} options.inputs
  @param {Output[]?} options.outputs
  @property {Number} version - Transaction version.
  @property {Number} flag - Flag field for segregated witness.
  Always non-zero (1 if not present).
  @property {Input[]} inputs
  @property {Output[]} outputs
  @property {Number} locktime - nLockTime
  @property {CoinView} view