+ /**
+ * Convenience method returning an attribute as a {@link String}.
+ *
+ * @param key the attribute name
+ * @return the attribute value as a {@link String} or <code>null</code>.
+ *
+ * @see Object#toString()
+ */
+ default String attr(QNamed key) {
+ return attr(key.qName());
+ }
+
+ /**
+ * Convenience method returning an attribute as a {@link String}.
+ *
+ * @param key the attribute name
+ * @return the attribute value as a {@link String} or <code>null</code>.
+ *
+ * @see Object#toString()
+ */
+ default String attr(String key) {
+ return attr(unqualified(key));