Cron Expression confusion in the Spring Framework

Question

Hello!

My scheduler's application context defines this trgger:

<bean id="myTrigger" class="org.springframework.scheduling.quartz.CronTriggerBean">
   <property name="jobDetail" ref="myJob"/>
   <property name="cronExpression" value="0 0 ∗ ∗ ∗ ?"/>
</bean>

Does it fire every day at 00:00? Or every hour? I'd say the latter, but the documentation of this project says otherwise... Can you help me out? Are there different kind of expressions?