+ * Registers custom relation in this parser. Note that when a custom relation
+ * is registered the parser is no longer strictly compliant with the chosen spec.
+ * @param relation
+ * @return true if custom relation has not been registered already
+ */
+ public boolean registerCustomRelation(String relation) {
+ return customRelations.add(relation);
+ }
+
+ /**
+ * Unregisters previously registered custom relation in this instance of the parser.
+ * @param relation
+ * @return true is relation has been previously registered
+ */
+ public boolean unregisterCustomRelation(String relation) {
+ return customRelations.remove(relation);
+ }
+
+ /**