I can't see any change when I use the *margin* option in the properties of an array. (pd extented 0.42.5 ; win7). Where's the problem ?

I don't think it's actually used in arrays. It's meant for GOP abstractions. Arrays are kind of like GOP versions of

Ok, thank you a lot. So array's use specific GOP which doesn't have the same functionality than other GOP, but they have the same properties dialog. little bit strange. thx.