The spec is open to interpretation about how alternatives are enabled. One popular interpretation is that alternatives must be enabled within the same bean archive that contains the alternative bean. However, it might be worth considering the merit of enabling an alternative from a deployment archive that contains the bean archive.
For example, suppose we have the following deployment archive:
It may be worth allowing AlternativeBean.class (a class annotated with @Alternative) to be enabled by listing it in the <alternatives> section of foo.war/WEB-INF/beans.xml.