Close issue #6210: Implement PEP 409
diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index c7252ed..fd7aee7 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -421,17 +421,24 @@
.. c:function:: PyObject* PyException_GetCause(PyObject *ex)
- Return the cause (another exception instance set by ``raise ... from ...``)
- associated with the exception as a new reference, as accessible from Python
- through :attr:`__cause__`. If there is no cause associated, this returns
- *NULL*.
+ Return the cause (either an exception instance, or :const:`None`,
+ set by ``raise ... from ...``) associated with the exception as a new
+ reference, as accessible from Python through :attr:`__cause__`.
+
+ If there is no cause associated, this returns *NULL* (from Python
+ ``__cause__ is Ellipsis``). If the cause is :const:`None`, the default
+ exception display routines stop showing the context chain.
.. c:function:: void PyException_SetCause(PyObject *ex, PyObject *ctx)
Set the cause associated with the exception to *ctx*. Use *NULL* to clear
- it. There is no type check to make sure that *ctx* is an exception instance.
- This steals a reference to *ctx*.
+ it. There is no type check to make sure that *ctx* is either an exception
+ instance or :const:`None`. This steals a reference to *ctx*.
+
+ If the cause is set to :const:`None` the default exception display
+ routines will not display this exception's context, and will not follow the
+ chain any further.
.. _unicodeexceptions: