Chapter 2. Develop Windows Store apps
One of the unique characteristics of a great Windows Store app is its capability to interact with other apps and Windows 8 through extensions and contracts. Extensions provide a way to extend or customize capabilities of Windows features within Windows Store apps. Contracts ensure that diverse apps present features, such as sharing an item through another app, using the same interface.
An extension enables an app to integrate with Windows and extend features provided by the operating system. Developers can extend features such as picking contacts and associating specific file types with specific criteria within their own app and potentially make their implementation available to other apps and Windows.
A contract ...