Point out difference between zero area and primitivesVisible = false

chapters/annotations.tex

@@ -749,7 +749,9 @@ \subsection{Extends-Clause}\label{extends-clause}
 \end{itemize}
 
 \begin{nonnormative}
-A zero area \lstinline!extent! other than \lstinline!{{0, 0}, {0, 0}}! will result in the base class contents not being visible.
+A zero area \lstinline!extent! other than \lstinline!{{0, 0}, {0, 0}}! will result in none of the base class contents being visible.
+By affecting components and connections as well as graphical primitives, this is different from setting \lstinline!primitivesVisible = false!.
+
 Reversed corners of the \lstinline!extent! will result in mirrored (rotated if reversed in both direction) base class contents.
 \end{nonnormative}