How do you create a Group in Address Book???

In the Properties of AB set Grouping by field "category" and you get groups.

Ah, now I see how this works, but it's a little bit confusing... I had set the option group by field to "Category", but nothing seemed to happen... only now I discovered I also had to set the grouping type to "Group by field".

This could be easily solved by disabling the "Group by field" option when it's not the selected "Grouping type"... Then it's obvious that this option has no effect...