Ignore flags on Py_slot_end

`Py_slot_invalid` with OPTIONAL can be used as a no-op slot

Author: encukou

peps/pep-0820.rst

@@ -368,8 +368,8 @@ Flags
   Effectively, consecutive slots with the HAS_FALLBACK flag, plus the first
   non-HAS_FALLBACK slot after them, form a “block” where the the interpreter
   will only consider the *first* slot in the block that it understands.
-  If the entire block is to be optional, it should end with a ``Py_slot_end``
-  with the OPTIONAL flag.
+  If the entire block is to be optional, it should end with a
+  slot with the OPTIONAL flag.
 
 - ``PySlot_IS_PTR``: The data is stored in ``sl_ptr``, and must be cast to
   the appropriate type.
@@ -447,18 +447,15 @@ New slot IDs
 The following new slot IDs, usable for both type and module
 definitions, will be added:
 
-- ``Py_slot_end`` (defined as ``0``)
+- ``Py_slot_end`` (defined as ``0``): Marks the end of a slots array.
 
-  - With ``sl_flags=Py_SLOT_OPTIONAL``, this slot is ignored.
-    Otherwise, this slot marks the end of the slots array.
-  - The ``PySlot_INTPTR`` flag is ignored.
-  - Other flags ( ``PySlot_STATIC``, ``PySlot_HAS_FALLBACK``) are
-    not allowed with ``Py_slot_end``.
+  - The ``PySlot_INTPTR`` and ``PySlot_STATIC`` flags are ignored.
+  - The ``PySlot_OPTIONAL`` and ``PySlot_HAS_FALLBACK`` flags are not
+    allowed with ``Py_slot_end``.
 
 - ``Py_slot_subslots``, ``Py_tp_slots``, ``Py_mod_slots``: see
   *Nested slot tables* above
-- ``Py_slot_invalid``: treated as an unknown slot ID. (Useful for testing
-  how optional and fallback slots work.)
+- ``Py_slot_invalid``: treated as an unknown slot ID.
 
 The following new slot IDs will be added to cover existing
 members of ``PyModuleDef``: