diff --git a/Doc/extending/extending.rst b/Doc/extending/extending.rst
index 17c6fb224265ca..f9b65643dfe888 100644
--- a/Doc/extending/extending.rst
+++ b/Doc/extending/extending.rst
@@ -1084,7 +1084,14 @@ references to all its items, so when item 1 is replaced, it has to dispose of
 the original item 1.  Now let's suppose the original item 1 was an instance of a
 user-defined class, and let's further suppose that the class defined a
 :meth:`!__del__` method.  If this class instance has a reference count of 1,
-disposing of it will call its :meth:`!__del__` method.
+disposing of it will call its :meth:`!__del__` method. Internally,
+:c:func:`PyList_SetItem` calls :c:func:`Py_DECREF` on the replaced item,
+which invokes replaced item's corresponding
+:c:member:`~PyTypeObject.tp_dealloc` function. During
+deallocation, :c:member:`~PyTypeObject.tp_dealloc` calls
+:c:member:`~PyTypeObject.tp_finalize`, which is mapped to the
+:meth:`!__del__` method for class instances (see :pep:`442`). This entire
+sequence happens synchronously within the :c:func:`PyList_SetItem` call.
 
 Since it is written in Python, the :meth:`!__del__` method can execute arbitrary
 Python code.  Could it perhaps do something to invalidate the reference to
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 771e0f2709a4aa..30fd4db1fd1851 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -1764,7 +1764,7 @@ always available. Unless explicitly noted otherwise, all variables are read-only
    :func:`settrace` for each thread being debugged or use :func:`threading.settrace`.
 
    Trace functions should have three arguments: *frame*, *event*, and
-   *arg*. *frame* is the current stack frame.  *event* is a string: ``'call'``,
+   *arg*. *frame* is the :ref:`current stack frame <frame-objects>`. *event* is a string: ``'call'``,
    ``'line'``, ``'return'``, ``'exception'`` or ``'opcode'``.  *arg* depends on
    the event type.