Which rule types do not have an "applies to" class?

The correct choice indicates that portal and skin rules do not have an "applies to" class. This is because portal and skin rules are more focused on the overall user experience and visual interface rather than being tied to a specific class structure.

Portal rules define how users interact with various applications at a high level, encompassing the layout, navigation, and general appearance without being bound to a specific business object or data class. Skin rules dictate the styling and design elements applied throughout the user interface, ensuring consistency across the application. As they serve a universal function, both rule types operate independently of any specific class context, thus lacking an "applies to" class.

In contrast, flow actions, data types, and user interface rules are connected to specific classes because they are fundamentally designed to interact with or manipulate the data and processes associated with those classes. Flow actions, for example, are closely tied to the actions that can be performed on an instance of a class, while data types provide a structure for the data model that supports those instances. User interface rules are essential for defining interfaces that pertain to specific classes, thereby necessitating an "applies to" context.