private static void mergeInto(Element destination, List<Element> subElements) {
        // System.out.println("merging " + subElements.size() + " elements into " + destination.getTagName());
        for (Element subElement : subElements) {
            Node copiedNode = destination.getOwnerDocument().importNode(subElement, true);
            destination.appendChild(copiedNode);
        }
    }
Handles preprocess:include statements and returns a Document which has all the include statements resolved

@author hmusum
config-application-package/src/main/java/com/yahoo/config/application/IncludeProcessor.java