Clarifications

Author: Daniel Sperber

peps/pep-0821.rst

@@ -76,7 +76,7 @@ Allowing ``Unpack[TypedDict]`` inside ``Callable`` achieves the following:
   with existing semantics from :pep:`692` (``Unpack`` for ``**kwargs``) and
   :pep:`728` (``extra_items`` and ``closed``).
 * Keeps the feature additive, backwards compatible, and stays mostly a
-  typing-specification change only.
+  typing-specification change only, see `Backwards Compatibility`_.
 
 Alternatives considered
 -----------------------
@@ -104,11 +104,17 @@ Design trade-offs and decisions
 * Positional parameters: Allowing positional parameters to precede
   ``Unpack[TD]`` retains existing ``Callable`` semantics and mirrors real
   Python functions where positional and keyword-only parameters coexist.
-* ``Concatenate``: ``Unpack[TD]`` cannot appear within ``Concatenate``
+
+* ``Unpack[TD]`` cannot appear within ``Concatenate``
   (e.g. ``Concatenate[int, Unpack[TD], P]``), as this would enable
   interspersed keyword-only parameters among ``*args`` and ``**kwargs``.
   This increases complexity and is not proposed here.
 
+* Abbreviation with ``**``: This PEP does not add a suggestion to add a ``**``
+  shorthand (e.g. ``**TD``) for ``Unpack[TD]`` in ``Callable``. The proposal
+  is intentionally minimal, reusing the existing ``Unpack[TD]`` form. Adding
+  such an abbreviation would require a grammar change and is out of scope.
+
 Specification
 =============
 
@@ -167,18 +173,18 @@ rejected::
 Interaction with ``ParamSpec``, ``TypeVarTuple``, and ``Concatenate``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-``Unpack[TD]`` cannot appear within ``Concatenate``
-(e.g. ``Concatenate[int, Unpack[TD], P]``); use
-``Callable[[int, Unpack[TD]], R]`` instead.
-See `Design trade-offs and decisions`_ for the rationale.
-
 A ``TypeVarTuple`` may coexist with ``Unpack[TD]`` in the parameter list,
 because ``TypeVarTuple`` corresponds to ``*args`` and does not interfere
 with the ``**kwargs``-equivalent role of ``Unpack[TD]``::
 
-    # Tv is a TypeVarTuple, e.g. in class F[*Tv]: ...
+    # With Tv a TypeVarTuple
     Callable[[Unpack[Tv], Unpack[KeywordTD]], R]  # Allowed
 
+``Unpack[TD]`` cannot appear within ``Concatenate``
+(e.g. ``Concatenate[int, Unpack[TD]]``); use
+``Callable[[int, Unpack[TD]], R]`` instead.
+See `Design trade-offs and decisions`_ for the rationale.
+
 A ``ParamSpec`` may not appear alongside ``Unpack[TD]`` in the same
 ``Callable`` parameter list, because ``ParamSpec`` covers both ``*args``
 and ``**kwargs``, which conflicts with ``Unpack[TD]``::