Issue 27366: PEP 487 docs updates

- Porting note for type keyword arg handling
- __init_subclass__ note regarding  metaclass hint

Doc/reference/datamodel.rst

@@ -1672,6 +1672,13 @@ class defining the method.
    The default implementation ``object.__init_subclass__`` does
    nothing, but raises an error if it is called with any arguments.
 
+   .. note::
+
+      The metaclass hint ``metaclass`` is consumed by the rest of the type
+      machinery, and is never passed to ``__init_subclass__`` implementations.
+      The actual metaclass (rather than the explicit hint) can be accessed as
+      ``type(cls)``.
+
    .. versionadded:: 3.6
 
 

Doc/whatsnew/3.6.rst

@@ -759,6 +759,15 @@ Changes in the Python API
   <keyword-only_parameter>`.
   (Contributed by Serhiy Storchaka in :issue:`18726`.)
 
+* As part of :pep:`487`, the handling of keyword arguments passed to
+  :class:`type` (other than the metaclass hint, ``metaclass``) is now
+  consistently delegated to :meth:`object.__init_subclass__`. This means that
+  :meth:`type.__new__` and :meth:`type.__init__` both now accept arbitrary
+  keyword arguments, but :meth:`object.__init_subclass__` (which is called from
+  :meth:`type.__new__`) will reject them by default. Custom metaclasses
+  accepting additional keyword arguments will need to adjust their calls to
+  :meth:`type.__new__` (whether direct or via :class:`super`) accordingly.
+
 
 Changes in the C API
 --------------------