synchronized public
	void addElementWithReplacement (Element e) {
		Element root = doc.getRootElement();
		
		Collection<Element> oldCachedElements = queryXPathList(
				String.format(ELEMENT_BY_URL_XPATH,e.getAttributeValue("url")));
		for (Element current: oldCachedElements) 
			current.detach();

		root.addContent((Element)e.clone());
	}