PEAR::DB and transactions

I have a program I'm writing that needs to use transactions if that feature is supported by the DBMS. In reading here: http://pear.php.net/manual/en/package.database.db.db-common.provides.php I see I can check if the DBMS supports transaction which is great. However, I don't see anything here: http://pear.php.net/manual/en/package.database.php that suggests how to wrap things into a transaction. Obviously the fact provides() even exists tells me there is some methods in the PEAR::DB manual that isn't showing up that is probably here. So my question is, how to I start, stop and rollback transactions with PEAR::DB? Thanks, --Tony