private List<Element> allChainElements(DeployState deployState, Element chainsElement) {
        List<Element> chainsElements = new ArrayList<>();
        chainsElements.add(chainsElement);

        return chainsElements;
    }
NOTE: This class _must_ be abstract, due to calling subclass method in ctor.
@author Tony Vaagenes
@author gjoranv
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/DomChainsBuilder.java