Playgrounds can contain a mix of code and documentation. This allows a set of code, samples, and explanations to be mixed in with the playground itself.
As playgrounds can contain a mixture of code and documentation, it makes them an ideal format to view annotated code snippets. In fact, Apple's Swift Tour book can be opened as a playground file.
Xcode documentation can be searched by navigating to Help | Documentation and API Reference or by pressing Command + Shift + 0. In the search dialog that is presented, type
Swift Tour and then select the first result. The Swift Tour book should be presented in Xcode's help system, as follows:
A link to download and open the documentation as a playground ...