s.colby. It is prefixed automatically by your developer Team ID.
When the user connects to iCloud (usually this happens through the iCloud System Preference panel whenever the user logs in), the Apple ID is made available to all apps that are entitled to use iCloud. The ubiquity container identifier is usually set in the Capabilities tab of the target in Xcode. As you will see in Chapter 18, “Completing the Round Trip,” a shared ubiquity container may have an identifier that does not correspond to an app bundle identifier. In the case of the Round Trip, the two apps are com.champlainarts.ColbyOSX and com.champlainarts.ColbyiOS. They share a ubiquity container called com.champlainarts.Colby. It is the last component of the ubiquity container identifier that shows up in the System Preferences iCloud pane shown previously at the left in Figure 1.5.
With these two pieces of information, you can connect to the appropriate iCloud ubiquity container. That is your first task when your app starts to run.