diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -306,6 +306,8 @@
    foundation for higher level context managers that manipulate the exit
    stack in application specific ways.
 
+   The :meth:`__enter__` method of an instance trivially returns itself.
+
    .. versionadded:: 3.3
 
    .. method:: enter_context(cm)