private Tags getTags(Element element) {
        String env = element.getAttributeNS(XmlPreProcessor.deployNamespaceUri, TAGS_ATTRIBUTE);
        if (env.isEmpty()) return Tags.empty();
        return Tags.fromString(env);
    }
Retains all elements where at least one element is overridden. Removes non-overridden elements from map.
config-application-package/src/main/java/com/yahoo/config/application/OverrideProcessor.java