A car company uses Author, and is using the metadata plugin. They've created the variables Version and Features. Version refers to whether a car is a basic or advanced model, features refers to what features the car has. Advanced models have access to more features than basic models.
This company uses the Metadata plugin to limit the values an author can assign to the Feature variable when the Version variable is assigned the value Basic. This prevents authors from assigning advanced features to topics about basic models.