code: public boolean parseUnrecognizedElement(final Element element,
                                            final Properties props) throws Exception {
        final String nodeName = element.getNodeName();
        if ("filter".equals(nodeName)) {
            OptionHandler filter =
                    org.apache.log4j.extras.DOMConfigurator.parseElement(
                            element, props, Filter.class);
            if (filter instanceof Filter) {
                filter.activateOptions();
                this.addFilter((Filter) filter);
            }
            return true;
        }
        return false;
    }
docs: {@inheritDoc}