Current documentation for clustered singleton mdb [1] should be more like it's described in [2] where the description is described in more detail.

Additionally we should mention in which maven dependency annotations:
@org.jboss.ejb3.annotation.ClusteredSingleton
@org.jboss.ejb3.annotation.DeliveryGroup

are located:

 <dependency>
            <groupId>org.jboss.ejb3</groupId>
            <artifactId>jboss-ejb3-ext-api</artifactId>
            <version>2.2.0.Final</version>
        </dependency>

[1] https://access.redhat.com/documentation/en/red-hat-jboss-enterprise-application-platform/version-7.0/developing-ejb-applications/#clustered_singleton_mdbs
[2] https://docs.jboss.org/author/display/WFLY10/Message+Driven+Beans+Controlled+Delivery