code: public <E extends Element> List<E> filterElements(Class<E> clazz) {
  		synchronized(lock) {
  			if(elements == null) return Collections.emptyList();
  			return AoCollections.filter(elements, clazz);
  		}
  	}
docs: Gets all elements in the page (including all child elements) that are of the
  given type, in the order they were declared in the page.