note that descriptor objects must be instances of new-style types
(closes SF bug #817742)
diff --git a/Doc/ref/ref3.tex b/Doc/ref/ref3.tex
index 1daf18a..9cd7a4c 100644
--- a/Doc/ref/ref3.tex
+++ b/Doc/ref/ref3.tex
@@ -1296,7 +1296,8 @@
the class dictionary of another new-style class, known as the
\emph{owner} class. In the examples below, ``the attribute'' refers to
the attribute whose name is the key of the property in the owner
-class' \code{__dict__}.
+class' \code{__dict__}. Descriptors can only be implemented as
+new-style classes themselves.
\begin{methoddesc}[object]{__get__}{self, instance, owner}
Called to get the attribute of the owner class (class attribute access)