public static List<Element> mergeElems(Element parent, String name, ApplicationPackage app, String pathFromAppRoot) {
        List<Element> children = XML.getChildren(parent, name);
        List<Element> allFromFiles = allElemsFromPath(app, pathFromAppRoot);
        for (Element fromFile : allFromFiles) {
            children.addAll(XML.getChildren(fromFile, name));
        }
        return children;
    }
Will get all sub-elements under parent named "name", just like XML.getChildren(). Then look under
pathFromAppRoot/ in the app package for XML files, parse them and append elements of the same name.

@param parent parent XML node
@param name name of elements to merge
@param app an {@link ApplicationPackage}
@param pathFromAppRoot path from application root
@return list of all sub-elements with given name
config-application-package/src/main/java/com/yahoo/config/application/Xml.java