Some cleanup in the docs.
diff --git a/Doc/library/constants.rst b/Doc/library/constants.rst
index 4aa3a1c..7e63978 100644
--- a/Doc/library/constants.rst
+++ b/Doc/library/constants.rst
@@ -25,6 +25,9 @@
represent the absence of a value, as when default arguments are not passed to a
function.
+ .. versionchanged:: 2.4
+ Assignments to ``None`` are illegal and raise a :exc:`SyntaxError`.
+
.. data:: NotImplemented
@@ -37,5 +40,11 @@
Special value used in conjunction with extended slicing syntax.
- .. % XXX Someone who understands extended slicing should fill in here.
+ .. XXX Someone who understands extended slicing should fill in here.
+
+.. data:: __debug__
+
+ This constant is true if Python was not started with an :option:`-O` option.
+ Assignments to :const:`__debug__` are illegal and raise a :exc:`SyntaxError`.
+ See also the :keyword:`assert` statement.
\ No newline at end of file