[Zope] for ... in or aq_acquire arguments ?

in this line for data in self.aq_acquire('_getProductRegistryData')('zclasses'): i suppose that aq_acquire returns the value of _getProductRegistryData of self but what is "'zclasses'" is it anargumet for the for loop or for the aq_acquire method ? I serached for the syntax of aq_acquire and for..in and i did'nt find this syntax for expression in (expression_list) (something_else): TIA -- Andre PZP Enthusiast