Add a SubprocessError base class for exceptions in the subprocess module.
diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index bb6e68b..6ea3c10 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -387,6 +387,11 @@
:func:`call` and :meth:`Popen.communicate` will raise :exc:`TimeoutExpired` if
the timeout expires before the process exits.
+Exceptions defined in this module all inherit from :ext:`SubprocessError`.
+
+ .. versionadded:: 3.3
+ The :exc:`SubprocessError` base class was added.
+
Security
^^^^^^^^