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

[D2]

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