Issue #13302: backport part of 3ed28f28466f

Doc/c-api/arg.rst

@@ -24,6 +24,11 @@ the format unit; the entry in (round) parentheses is the Python object type
 that matches the format unit; and the entry in [square] brackets is the type
 of the C variable(s) whose address should be passed.
 
+These formats allow to access an object as a contiguous chunk of memory.
+You don't have to provide raw storage for the returned unicode or bytes
+area.  Also, you won't have to release any memory yourself, except with the
+``es``, ``es#``, ``et`` and ``et#`` formats.
+
 ``s`` (string or Unicode) [const char \*]
    Convert a Python string or Unicode object to a C pointer to a character
    string.  You must not provide storage for the string itself; a pointer to