Xcode project inside project
They are called cross project references. From the link below:
Cross-project references are a convenient way to create relationships between two separate Xcode projects.
One method of creating shared frameworks is using sub-projects. You can also do it with single projects. More here:
Other links:
cross-project references aka project in project aka sub-project aka nested projects.This approach uses Explicit dependency[About] [How to setup]
If you already have separate Xcode projects for your framework and application, you can take advantage of Xcode’s cross-project references to embed the framework in your application. Cross-project references are a convenient way to create relationships between two separate Xcode projects.
To define explicit dependencies between targets in separate project files, project files should be nested. This means that a target can set explicit dependencies of any other target within the same project file, or any nested child project file.
In XCode 4, the idea of workspaces[About] is supposed to supersede the functionality of XCode 3s cross-project references