All Known Subinterfaces:

AlternateLanguageExtension, GoogleImageExtension, GoogleNewsExtension, GoogleVideoExtension

All Known Implementing Classes:

AbstractExtension
```
@ProviderType
public interface Extension
```
A marker interface used as consumer facing API for custom extensions.
Implementations must extend this interface to provide a sub type of it that can be added to a Url using Url.addExtension(Class).

Interface Extension