If you have individual readers logging in to your knowledge base, Reader Groups allow you to display content only to specific groups and assign which readers should see which content.
Use the Restrict to Groups option to restrict the current article or category to any of the reader groups in your knowledge base.
If you use the Restrict to Groups option for a category, all subcategories and articles within the category inherit these restrictions.
If this section shows Add More Restrictions, this content is already inheriting reader group restrictions from one of the categories it belongs to. Adding more groups in this section means that a reader must be a member of one of the Inherited Restrictions groups AND a member of one of the Add More Restrictions groups.
See How do reader groups work? for more information on working with reader groups.
