Issue #9738: PyUnicode_FromFormat() and PyErr_Format() raise an error on
a non-ASCII byte in the format string.
Document also the encoding.
diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index fcbd50b..f969b96 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -146,7 +146,7 @@
.. cfunction:: PyObject* PyErr_Format(PyObject *exception, const char *format, ...)
This function sets the error indicator and returns *NULL*. *exception* should be
- a Python exception (class, not an instance). *format* should be a string,
+ a Python exception (class, not an instance). *format* should be an ASCII-encoded string,
containing format codes, similar to :cfunc:`printf`. The ``width.precision``
before a format code is parsed, but the width part is ignored.