Decorators cannot declare observers, producers and disposers according to:

Interceptors and decorators may not declare producer methods. If an interceptor or decorator has a method annotated @Produces , the container automatically detects the problem and treats it as a definition error.

and

Interceptors and decorators may not declare observer methods. If an interceptor or decorator has a method with a parameter annotated @Observes , the container automatically detects the problem
and treats it as a definition error.

The question is whether following restriction (basically second sentence) is unnecessary because all conditions (in which this could happen) are already excluded in the above restrictions.

The delegate injection point must be an injected field, initializer method parameter or bean constructor method parameter. If an injection point that is not an injected field, initializer method parameter or bean constructor method parameter is annotated @Delegate , the container
automatically detects the problem and treats it as a definition error.