Elaborate that sizeof only accounts for the object itself.
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 55c06ca..c7b3ea9 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -441,6 +441,9 @@
does not have to hold true for third-party extensions as it is implementation
specific.
+ Only the memory consumption directly attributed to the object is
+ accounted for, not the memory consumption of objects it refers to.
+
If given, *default* will be returned if the object does not provide means to
retrieve the size. Otherwise a :exc:`TypeError` will be raised.