PEP 728: Address additional feedback (#4383)

Address feedback from Eric.

https://discuss.python.org/t/pep-728-typeddict-with-typed-extra-items/45443/150

Author: PIG208

peps/pep-0728.rst

@@ -240,7 +240,12 @@ The ``closed`` Class Parameter
 ------------------------------
 
 When neither ``extra_items`` nor ``closed=True`` is specified, ``closed=False``
-is assumed.
+is assumed. The TypedDict should allow non-required extra items of value type
+``ReadOnly[object]`` during inheritance or assignability checks, to
+preserve the default TypedDict behavior. Extra keys included in TypedDict
+object construction should still be caught, as mentioned in TypedDict's
+`typing spec
+<https://typing.python.org/en/latest/spec/typeddict.html#supported-and-unsupported-operations.>`__.
 
 When ``closed=True`` is set, no extra items are allowed. This is equivalent to
 ``extra_items=Never``, because there can't be a value type that is assignable to
@@ -293,13 +298,6 @@ argument is a read-only type::
 This will be further discussed in
 :ref:`a later section <pep728-inheritance-read-only>`.
 
-The TypedDict should allow non-required extra items of value type
-``ReadOnly[object]`` during inheritance or assignability checks, to
-preserve the default TypedDict behavior. Extra keys included in TypedDict
-object construction should still be caught, as mentioned in TypedDict's
-`typing spec
-<https://typing.python.org/en/latest/spec/typeddict.html#supported-and-unsupported-operations.>`__.
-
 ``closed`` is also supported with the functional syntax::
 
     Movie = TypedDict("Movie", {"name": str}, closed=True)
@@ -331,13 +329,21 @@ For type checking purposes, ``Unpack[SomeTypedDict]`` with extra items should be
 treated as its equivalent in regular parameters, and the existing rules for
 function parameters still apply::
 
-    class Movie(TypedDict, extra_items=int):
+    class MovieNoExtra(TypedDict):
         name: str
 
-    def f(**kwargs: Unpack[Movie]) -> None: ...
+    class MovieExtra(TypedDict, extra_items=int):
+        name: str
+
+    def f(**kwargs: Unpack[MovieNoExtra]) -> None: ...
+    def g(**kwargs: Unpack[MovieExtra]) -> None: ...
 
     # Should be equivalent to:
-    def f(*, name: str, **kwargs: int) -> None: ...
+    def f(*, name: str) -> None: ...
+    def g(*, name: str, **kwargs: int) -> None: ...
+
+    f(name="No Country for Old Men", year=2007) # Not OK. Unrecognized item
+    g(name="No Country for Old Men", year=2007) # OK
 
 Interaction with Read-only Items
 --------------------------------