MySQL: did anyone start a transaction?

Hello all, I asked this question on php-general last month (http://marc.info/?t=124049230300004&r=1&w=2), and received some answers -- but I was directed to this list, so here. My question is: can I tell programatically whether the next query I'm going to execute is already part of a transaction, using MySQL? The context is thus: I'm writing a PHP library which attempts to seamlessly merge database objects and PHP objects. Architecture discussion aside (which I'm more than open to, if anyone cares enough to talk), I need to know whether the code outside the library has already started a transaction or not. I need to know that because I need to execute both PHP and SQL from a single external call -- if either one of my internal PHP or SQL calls fail, I need to revert to the original state before the external call. And since transactions can't be nested, I can't unconditionally start a new transaction when the external call is being initiated -- therefore I need to know whether the programmer has already started a transaction or not. Thank you, Bogdan