[Zope] Calling objects with arguments in a sequence

Hi I'm using the Photo product, instances of which I can call, with arguments, like this: <dtml-var "my_photo(display='thumbnail')"> However, I can't work out how to pass arguments to each sequence item when iterating over a sequence. For example, I've tried: <dtml-in objectValues(['Photo'])"> <dtml-var "_['sequence-item'](display='thumbnail')"> </dtml-in> (..not that I expect that to work :) And I get Error Type: TypeError Error Value: call of non-function (type string) I've tried various combinations of ways of calling the sequence-item, but they all return the same error. Could anyone suggest how I should do this? Thanks in advance... Seb