Master-Detail scenario on a module basis means that switching between items in accordion control (WPF Toolkit) changes modules and views accordingly. Each module contains two views one registered to the left hand side region (ToolRegion) and another one assigned to the right hand side region (DockRegion). To be more specific an opening of a particular item in accordion control causes an activation of a second view from the same module. DocRegion contains multiple views but only one can be visible at a time and an activation is a process which tells a region what to show.
A module in the Composite Application Library is a logical unit in your application. Modules assist in implementing a modular design. These modules are defined in such a way that they can be discovered and loaded by the application at run time. Because modules are self-contained, they promote separation of concerns in your application. Modules can communicate with other modules and access services in a loosely coupled fashion. They reduce the friction of maintaining, adding, and removing system functionality. Modules also aid in testing and deployment.
Region is a slot/place holder in your window/shell space where a view can be registered. Region is view agnostic and collaborates with Region Adapter to deal with views. The power of regions comes in their ability to hold any type of UI content. A module can contain UI content manifested as a user control, a data type that is associated with a data template, a custom control, or any combination of these.
In the following example modules don't know about one another and don't communicate with themselves (communication between modules is possible based on EventAggregator). Modularity is the most useful aspect of this solution so modules can be loaded dynamically depends on predefined conditions creating a cohesive and flexible interface.
Source code (VS2010): MasterDetail.zip