How do I treat the drop-down country list to specify that I am looking for French/Italian co-productions (i.e. I want to include two countries, but only those films which are registered as both)?
In the Advanced Title Search page, scroll down to Countries and select the co-producing countries. You need to click on the first one, then Ctrl-click on the second.
Make any other restrictions you want (e.g. Feature films only), select the sort you prefer, then click on the Search button at the bottom of the page.
I ran with the Feature Film restriction and got :
Feature Films With Country of Origin France/Italy
Sorted by Title Ascending
1-50 of 2,456
titles.