Hi oosyrag,
Many thanks for all your help. The project's still too early in development for me to have a really clear idea about the interface, but once I've given it more thought I'll post a sample image and description when I have time.
If I decide to stick with drag and drop I doubt I'll use more than three items as I could see it was starting to get overly complex.
In the meantime, here's my attempt at adding a third item. I've added the "For each item family" but still can't get them to combine.
According to debug mode the "ID2Valid" and "ID3Valid" variables don't always switch to "True" when overlapping the other items.
drive.google.com/file/d/12kvwVJnoTaVl5K5gLJEllirUFHkhvmPy/view