@@ 74,7 74,14 @@ signature BLOCK_STREAM = sig
 
     type new_args
 
-    (** Construct a new stream. *)
+    (** Construct a new stream.
+
+        Many streams will also have a "wrap" function that accepts an
+        existing stream of some specific "upstream" type and creates
+        one of these streams to wrap it (i.e. providing output for
+        this stream based on the output of that stream). Because not
+        every stream has an "upstream" type or wraps anything, the
+        "wrap" function is not declared in this signature. *)
     val new : new_args -> stream
                  
 end