The Xcode Library is an easy way for you to discover available SwiftUI views and drag and drop them to the Xcode Previews canvas, enabling rich visual editing of your app. We’ll show you how to extend the content of the Xcode Library with your own views and modifiers, optimizing for reusability and discoverability within your app or Swift packages.
For more on Xcode Previews, check out "Structure your app for SwiftUI previews", and "Visually edit SwiftUI views".