code: func (db *DB) BeginTxx(ctx context.Context, opts *sql.TxOptions) (*Tx, error) {
  	tx, err := db.DB.BeginTx(ctx, opts)
  	if err != nil {
  		return nil, err
  	}
  	return &Tx{Tx: tx, driverName: db.driverName, unsafe: db.unsafe, Mapper: db.Mapper}, err
  }
docs: // BeginTxx begins a transaction and returns an *sqlx.Tx instead of an
  // *sql.Tx.
  //
  // The provided context is used until the transaction is committed or rolled
  // back. If the context is canceled, the sql package will roll back the
  // transaction. Tx.Commit will return an error if the context provided to
  // BeginxContext is canceled.