The category availability determines if the category can be displayed under what conditions. You must first enable the Availability feature under Configuration > Category menu.
The Storefront comes with several predefined rules such as allowing a category to be shown based on user location or security role.
The category availability rule can also use XSL transform to determine whether this category is available. For example, you may restrict the category to wholesale members on your site with a certain security role. The expected output should return "true" to indicate this product is available for sale under the input conditions, otherwise "false" if disallowed.
You can store additional information about the category using the Extension field and XML data. The extension information automatically becomes available for query in your business rules.
The Storefront comes with several pre-defined rules that you can simply modify the values without needing to know XSL. To learn more about XSL, please see the XSL Transform section.