Read original post by Michael Washington at LightSwitch Help Website
Visual Studio LightSwitch allows you to create Collection Control extensions. A Collection Control extension allows you to specify the control that will display a Entity collection in LightSwitch. At the time this article is written, there is no official documentation on creating Collection Control extensions. The only example of a Collection Control that Microsoft provides is the Many-To-Many control (see: Using The Many-To-Many Control).