code: function TransactionBuilder (network, maximumFeeRate) {
    this.prevTxMap = {}
    this.network = network || networks.bitcoin
  
    // WARNING: This is __NOT__ to be relied on, its just another potential safety mechanism (safety in-depth)
    this.maximumFeeRate = maximumFeeRate || 2500
  
    this.inputs = []
    this.tx = new Transaction(this.network)
  }
docs: By default, assume is a bitcoin transaction