With any group of categories, you need to know where to start when navigating. That starting point is called a root category.
Designate a category as a root category by setting the value of the rootCategories property of the catalog to include the category you want to be considered the top level of the product catalog. The allRootCategories property of the user’s catalog specifies all the categories in a catalog’s rootCategories property.
Note: Root categories of a “root sub catalog” are also considered root categories. For example, if Catalog A has Catalog B as a “Sub catalog at root” then allRootCategories of Catalog B are included in the allRootCategories of Catalog A.
See the Catalog Navigation and Searching chapter of the ATG Commerce Guide to Setting Up a Store for an example of using this targeter to find root categories.
