According to the product team, they are authored by Twitter’s curation group. In our testing, annotations only appear on the mobile app and not on the same Moments on desktop.

Annotations were retired in May 2017. Users haven’t been able to create or edit annotations since then, but existing annotations were still shown to desktop viewers.

Annotations are meant to be processed; otherwise, there’s no point in having them. Java 5 extended the Java Reflection API to help you create your own annotation processing tools.