In order to ensure that the right item is sorted into the desired category, you can define here which condition by category must be met for the sort function. As a standard, however, items are sorted by their descriptions into individual categories. For example, when you add an item such as "Bon Jovi Maxi CD" as well as an item such as "Whitney Houston Single-CD", both will be placed in the category "CD". In addition, you can also define which items you don't want to include or which item containing a specific description you would like to include in your gallery.