[development] Question about error_reporting()

Hi guys, I am looking at the implementation of error_reporting: http://api.drupal.org/api/function/error_handler/5 and I don't understand this line: if ($errno & (E_ALL ^ E_NOTICE)) { does it means that all errors but E_NOTICE are gonna be reported ? (what I really dont get is the meaning of the ^ php operator....).... I am trying to understand this code because my watchdog table is getting full of PHP warning messages, and I was not able to found a configuration option to filter this kind of messages. Would it be possible to change the behaviour to report messages above or below a specific level like it is done in php.ini ? Thanks in advance.