Ceum sometimes turns new features on for a small group of users before releasing them to everyone. While a feature is in preview it may change, behave differently, or be turned off.
When an article describes a feature whose flag is not yet generally available, a preview notice appears at the top of the article. The notice disappears automatically once the feature becomes generally available — no documentation change is required.
This article is itself marked with the example-new-thing flag so you can see
how the preview notice behaves while that flag is in preview.