code: func newTxList(strict bool) *txList {
  	return &txList{
  		strict:  strict,
  		txs:     newTxSortedMap(),
  		costcap: new(big.Int),
  	}
  }
docs: // newTxList create a new transaction list for maintaining nonce-indexable fast,
  // gapped, sortable transaction lists.