How does $this->db->trans_status() work?

[eluser]Syed Rakib Al Hasan[/eluser]
[quote author="WanWizard" date="1341261683"]It's status is set to FALSE if a query fails, so if running a query returns FALSE.[/quote]
Thanks. I am interested to know HOW does dba->get_status() understand that it, in fact, is returning the correct status of the SQL? Is it based on SQL deadlock issues? Is it based on malformed SQL strings? Is it based on timeout issues? I actually have about 10 to 15 SQLs between a trans_start and trans_complete