Mark an annotation element as a directive.

This is used when applying Capability or Requirement as a meta annotation to an annotation declaration. The value of the annotation element annotated with Directive is used as the value of a directive in the generated capability or requirement clause. For example:

@Capability(namespace = "my.namespace")
public @interface MyCapability {
  @Directive("resource")
  String value() default "";
}

@MyCapability("foo")
public MyClass {}

The use of the MyCapability annotation, which is meta annotated with the Capability and Directive annotations, will result in a capability in the namespace my.namespace with the directive resource:=foo.

If the element annotated with Directive is unspecified when applied, then the directive must not be generated in the generated capability or requirement clause. For example:

@MyCapability
public MyClass {}

will not have the resource directive in the generated capability.

This annotation is not retained at runtime. It is for use by tools to generate bundle manifests.