Remove default, and update simulation model requirement for StopTime.

chapters/annotations.tex

@@ -392,15 +392,15 @@ \section{Annotations for Simulations}\label{annotations-for-simulations}
 record experiment
   Real StartTime(unit = "s") = 0;
   Real StopTime(unit = "s");
-  Real Interval(unit = "s") = $\ldots{}$;
-  Real Tolerance = $\ldots{}$;
+  Real Interval(unit = "s");
+  Real Tolerance;
 end experiment;
 \end{lstlisting}
 The \lstinline!experiment! annotation defines the start time (\lstinline!StartTime!) in {[}s{]}, the stop time (\lstinline!StopTime!) in {[}s{]}, the suitable time resolution for the result grid (\lstinline!Interval!) in {[}s{]}, and the relative integration tolerance (\lstinline!Tolerance!) for simulation experiments to be carried out with the model or block at hand.
 When \lstinline!Interval! or \lstinline!Tolerance! is not provided, the tool is responsible for applying appropriate defaults.
 If \lstinline!StartTime! is not specified it is assumed to be \lstinline!0.0!.
 
-If \lstinline!StopTime! is set the model should be a simulation model.
+If \lstinline!StopTime! is set the model is required to be a simulation model.
 Tools can allow users to override these settings without modifying the model.
 \end{semantics}
 \end{annotationdefinition}