The contents window provides also a number of advanced options from its pop-up menu . However, when it has children, its branch opens or closes. The main difference is that topics do not take part in repetitions but are only presented before learning a sequence of items. This helps to approach the subject as a whole before repetitions begin. For performance reasons, you should limit the number of elements per category to 50-100.
Children limit per hierarchy node .
To select a category, you have to choose it in the category combo box on the main toolbar.