PEP 3118: Add canonical-doc & mention unimplemented changes. (GH-4200)

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: encukou

peps/pep-3118.rst

@@ -5,7 +5,24 @@ Status: Final
 Type: Standards Track
 Created: 28-Aug-2006
 Python-Version: 3.0
-Post-History:
+Post-History: `09-Apr-2007 <https://mail.python.org/archives/list/python-dev@python.org/thread/X7A5IP4VFJTVCQJSMBXGAH3BVB3A5C3T>`__
+
+.. canonical-doc:: :external+python:ref:`bufferobjects`,
+                   :external+python:c:type:`PyBufferProcs`,
+                   :external+python:c:type:`PyMemoryView_FromObject`
+
+   Not all features proposed here were implemented. Specifically:
+
+   - ``PyObject_CopyToObject`` was not added.
+   - :ref:`3118-struct-additions` were not added, except for ``?`` (``_Bool``).
+   - ``PyObject_GetMemoryView`` is named
+     :external+python:c:type:`PyMemoryView_FromObject`.
+
+   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
 ========
@@ -626,6 +643,8 @@ 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
 =====================================