code: public function startTransaction(): bool
  	{
  		if ($this->isInTransaction) 
  			throw new AlreadyInTransactionException();
  		
  		$this->isInTransaction = $this->executeDirect('START TRANSACTION');
  		return $this->isInTransaction;
  	}
docs: Start a new transaction.
  @see https://dev.mysql.com/doc/refman/5.7/en/commit.html
  @return bool