Extra Categories pane is an additional control that extends the functionality of List View. This allows to classify records on the basis of their relationship with the current master object. Categories node is available in Application Model and you can quickly add an external classifier to any List View.
To see the Extra Categories in action, refer to the Main|Classifiers|Product section in the Xafari Northwind demo installed with Xafari. The Product object has a an Supplier reference property. The current Supplier object, selected in the Category panel, is used as the external classification for displayed Product objects.
Extra Categories feature is provided for the Win platform only. Extra Categories control depend on the Dock Panels and it is a mandatory requirement that the Dock Panels are supported in application.
To learn more about the Categories, refer to the following documents: