@@ -58,10 +58,13 @@
  *
  * @brief An abstract class for an unordered set of unique objects.
  *
  * @warning Do not mutate objects that are in a set! Changing the hash of
  *	    objects in a set breaks the internal representation of the set!
+ *
+ * @note Subclasses must implement @ref count, @ref containsObject: and
+ *	 @ref objectEnumerator.
  */
 @interface OFSet OF_GENERIC(ObjectType): OFObject <OFCollection, OFCopying,
     OFMutableCopying, OFSerialization>
 #if !defined(OF_HAVE_GENERICS) && !defined(DOXYGEN)
 # define ObjectType id