[docs] [issue17188] Document 'from None' in raise statement doc.

Nick Coghlan added the comment: As Terry notes, the various pieces of "from None" documentation should also have a nearby directive like: .. versionchanged: 3.3 :const:`None` permitted as ``Y`` in ``raise X from Y`` .. versionadded: 3.3 The ``__suppress_context__`` attribute to suppress automatic display of the exception context ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue17188> _______________________________________