Convention for package names in a custom plugin

Is there a convention for naming the Java packages within a custom Gradle plugin? I understand that the plugin ID should be namespaced with something unique to me, and have been using the form

However, for the actual Java/Groovy classes, is it conventional to put them in the org.gradle package, or continue to use my co.arichardson package? Putting them in org.gradle seems to have the nice benefit that things are auto-imported, but obviously carries some risk of name collision. The documentation also seems to suggest the org.gradle package, though not explicitly. Just wondering if there’s a defined best practice.

You should use your own packages (not org.gradle).