@@ -113,14 +113,18 @@ There are three ways strings and buffers can be converted to C:
113113``z `` (:class: `str ` or ``None ``) [const char \* ]
114114 Like ``s ``, but the Python object may also be ``None ``, in which case the C
115115 pointer is set to ``NULL ``.
116+ It is the same as ``s? `` with the C pointer was initialized to ``NULL ``.
116117
117118``z* `` (:class: `str `, :term: `bytes-like object ` or ``None ``) [Py_buffer]
118119 Like ``s* ``, but the Python object may also be ``None ``, in which case the
119120 ``buf `` member of the :c:type: `Py_buffer ` structure is set to ``NULL ``.
121+ It is the same as ``s*? `` with the ``buf `` member of the :c:type: `Py_buffer `
122+ structure was initialized to ``NULL ``.
120123
121124``z# `` (:class: `str `, read-only :term: `bytes-like object ` or ``None ``) [const char \* , :c:type: `Py_ssize_t `]
122125 Like ``s# ``, but the Python object may also be ``None ``, in which case the C
123126 pointer is set to ``NULL ``.
127+ It is the same as ``s#? `` with the C pointer was initialized to ``NULL ``.
124128
125129``y `` (read-only :term: `bytes-like object `) [const char \* ]
126130 This format converts a bytes-like object to a C pointer to a
@@ -377,6 +381,17 @@ Other objects
377381 Non-tuple sequences are deprecated if *items * contains format units
378382 which store a borrowed buffer or a borrowed reference.
379383
384+ ``unit? `` (anything or ``None ``) [*matching-variable(s) *]
385+ ``? `` modifies the behavior of the preceding format unit.
386+ The C variable(s) corresponding to that parameter should be initialized
387+ to their default value --- when the argument is ``None ``,
388+ :c:func: `PyArg_ParseTuple ` does not touch the contents of the corresponding
389+ C variable(s).
390+ If the argument is not ``None ``, it is parsed according to the specified
391+ format unit.
392+
393+ .. versionadded :: next
394+
380395A few other characters have a meaning in a format string. These may not occur
381396inside nested parentheses. They are:
382397
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