A card allows an application to export its application screen to another application. Unlike an application, which may offer a full and rich set of features, a card typically provides the ability to perform specific tasks such as picking a contact, composing an email or previewing an image. To a user, a card appears as part of the client application and does not appear separately in Active Frames. An application can embed only one card at a time. However, one card can embed another card, which allows the application to create a stack of cards that appear as part of the client application. Although the card appears as part of the client application, it maintains its own process and security context. In the following sections, you will learn how to create and use cards in your application, as well as how to expose them to other apps.