Historically, very few affordances were made when one developer wanted to communicate with the application data of another developer. URL schemes were manipulated for this purpose and they allowed a developer's app to be summoned by an identifier that was usually based on the bundle ID. In the last few major releases of iOS, there was at least the affordance for shared credentials to be accessed between apps by the same developer. This sharing of a keychain by an app group now also includes the sharing of file storage and preference data, which was previously accomplished by separate accounts with third-party sync services like Dropbox. iCloud Drive has been introduced to perform similar ad hoc file storage and sharing tasks. If this sounds somewhat limiting, it's because historically it has been, but we will touch upon the new ways in which app functionality and data can leak out from the one-app-at-a-time silo after we discuss how app data can now pass more easily between...