Change non-normative "For example, ..." to example

Addressing review comment by Hans.

chapters/classes.tex

@@ -248,10 +248,10 @@ \subsubsection{Prefix Rules}\doublelabel{prefix-rules}
 \lstinline!parameter! and \lstinline!constant! are described in \autoref{variability-of-structured-entities} for structured
 components.
 
-\begin{nonnormative}
-For example, \lstinline!input! can only be used, if none of the elements has a \lstinline!flow!, \lstinline!stream!, \lstinline!input! or
+\begin{example}
+\lstinline!input! can only be used, if none of the elements has a \lstinline!flow!, \lstinline!stream!, \lstinline!input! or
 \lstinline!output! type prefix.
-\end{nonnormative}
+\end{example}
 
 The prefixes \lstinline!input! and \lstinline!output! have a slightly different semantic meaning
 depending on the context where they are used: