[docs] [issue17422] language reference should specify restrictions on class namespace

Change by miss-islington <mariatta.wijaya+miss-islington@gmail.com>: ---------- pull_requests: +18170 pull_request: https://github.com/python/cpython/pull/18812 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue17422> _______________________________________