The online document is very simple but maybe too simple. It shows how to create a basic dialog WITHOUT tab, but formlayout in fact can do more, like building a tabbed dialog shown in the picture.

In the example shown in the picture, a and b are two simple lists which contain some keyword-value pairs. To create a dialog containing two tabs, we should make a combo list (so-called datagroup), in which each element is a list/tuple of three elements – (datalist, title_of_the_tab, comment_of_the_tab). Once the combo list is passed to formlayout, it shows a dialog like shown in the picture. We can categorize different imput groups in this way. Note the return value is also show in the picture, it’s a combo list too but only contains the values for the datalist.