Clarify that obsolete is not inherited.

Closes modelica#2338

chapters/annotations.tex

@@ -1123,6 +1123,10 @@ \section{Annotations for the Graphical User Interface}\doublelabel{annotations-f
 
 It indicates that the class ideally should not be used anymore and gives
 a message indicating the recommended action.
+This annotation is not inherited, the assumption is that if a class uses
+an obsolete class (as a base-class or as the class of one of the components) 
+that shall be updated - ideally without impacting users of the class.
+If that is not possible the current class can have also have an obsolete-annotation.
 
 A declaration may have the following annotations:
 \begin{lstlisting}[language=modelica]