The documentation listed in this page refers to the SettingsModel library project which is the project that implements the model of the settings engine and takes care of storage and retrieval to and from persistence.
The items on the right side of the graphic show the interface definition of each class. This is the API that consuming applications use to implement their customized SettingsModel.
XML Layer
The XML Layer class is currently invisible to the outside world but is listed here for the sake of completeness.