Annotations for class discovery and metadata description.
The Drupal plugin system has a set of reusable components that developers can use, override, and extend in their modules. Most of the plugins use annotations, which let classes register themselves as plugins and describe their metadata. (Annotations can also be used for other purposes, though at the moment, Drupal only uses them for the plugin system.)
To annotate a class as a plugin, add code similar to the following to the end of the d