gh-136032: Fix argparse.BooleanOptionalAction doc (#136133)

Doc/library/argparse.rst

@@ -839,23 +839,11 @@ how the command-line arguments should be handled. The supplied actions are:
     >>> parser.parse_args(['--version'])
     PROG 2.0
 
-Only actions that consume command-line arguments (e.g. ``'store'``,
-``'append'`` or ``'extend'``) can be used with positional arguments.
-
-.. class:: BooleanOptionalAction
-
-   You may also specify an arbitrary action by passing an :class:`Action` subclass or
-   other object that implements the same interface. The :class:`!BooleanOptionalAction`
-   is available in :mod:`!argparse` and adds support for boolean actions such as
-   ``--foo`` and ``--no-foo``::
-
-       >>> import argparse
-       >>> parser = argparse.ArgumentParser()
-       >>> parser.add_argument('--foo', action=argparse.BooleanOptionalAction)
-       >>> parser.parse_args(['--no-foo'])
-       Namespace(foo=False)
-
-   .. versionadded:: 3.9
+You may also specify an arbitrary action by passing an :class:`Action` subclass
+(e.g. :class:`BooleanOptionalAction`) or other object that implements the same
+interface. Only actions that consume command-line arguments (e.g. ``'store'``,
+``'append'``, ``'extend'``, or custom actions with non-zero ``nargs``) can be used
+with positional arguments.
 
 The recommended way to create a custom action is to extend :class:`Action`,
 overriding the :meth:`!__call__` method and optionally the :meth:`!__init__` and
@@ -1429,6 +1417,21 @@ this API may be passed as the ``action`` parameter to
       and return a string which will be used when printing the usage of the program.
       If such method is not provided, a sensible default will be used.
 
+.. class:: BooleanOptionalAction
+
+   A subclass of :class:`Action` for handling boolean flags with positive
+   and negative options. Adding a single argument such as ``--foo`` automatically
+   creates both ``--foo`` and ``--no-foo`` options, storing ``True`` and ``False``
+   respectively::
+
+       >>> import argparse
+       >>> parser = argparse.ArgumentParser()
+       >>> parser.add_argument('--foo', action=argparse.BooleanOptionalAction)
+       >>> parser.parse_args(['--no-foo'])
+       Namespace(foo=False)
+
+   .. versionadded:: 3.9
+
 
 The parse_args() method
 -----------------------