PEP 3118: Add canonical-doc & mention unimplemented changes.

peps/pep-3118.rst

@@ -10,6 +10,18 @@ Created: 28-Aug-2006
 Python-Version: 3.0
 Post-History:
 
+.. canonical-doc:: :external+python:ref:`bufferobjects`,
+                   :external+python:c:type:`PyBufferProcs`,
+                   :external+python:c:type:`PyMemoryView_FromObject`.
+
+   Some changes proposed here, like :ref:`3118-struct-additions` and
+   ``PyObject_CopyToObject``, were not implemented.
+   This PEP targets Python 3.0, which was released more than a decade ago.
+   Any proposals to add missing functionality should
+   be discussed as new features, not treated as finishing the implementation
+   of this PEP.
+
+
 Abstract
 ========
 
@@ -629,6 +641,8 @@ This will also be raised when a consumer requests a buffer from an
 object that does not provide the protocol.
 
 
+.. _3118-struct-additions:
+
 Additions to the struct string-syntax
 =====================================