Close bug 417930 by clarifying augmented assignment docs
diff --git a/Doc/ref/ref6.tex b/Doc/ref/ref6.tex
index 12261e2..80fae5a 100644
--- a/Doc/ref/ref6.tex
+++ b/Doc/ref/ref6.tex
@@ -300,6 +300,20 @@
possible \emph{in-place} behavior, the binary operation performed by
augmented assignment is the same as the normal binary operations.
+For targets which are attribute references, the initial value is
+retrieved with a \method{getattr()} and the result is assigned with a
+\method{setattr()}. Notice that the two methods do not necessarily
+refer to the same variable. When \method{getattr()} refers to a class
+variable, \method{setattr()} still writes to an instance variable.
+For example:
+
+\begin{verbatim}
+class A:
+ x = 3 # class variable
+a = A()
+a.x += 1 # writes a.x as 4 leaving A.x as 3
+\end{verbatim}
+
\section{The \keyword{pass} statement \label{pass}}
\stindex{pass}