Undertow appears to require explicit keywords implements WebApplicationInitializer

Undertow appears to require explicit keywords implements WebApplicationInitializer set on WEB-INF/classes when the class is using an "extends AbstractBaseClassThatImplementWebApplicationInitializer".

It does not appear to see the annotation set on the base class AbstractBaseClassThatImplementWebApplicationInitializer.

More over in my particular scenario this base class is provided in a JAR that is inside the EAR (not the WAR).

Maybe what Wildfly is doing is completely specification compliant and other Servlet implementations work differently.