Clarify final for classes. (#2719)

* Clarify final for classes.
Closes #2676
Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/inheritance.tex

@@ -547,6 +547,7 @@ \subsection{Final Element Modification Prevention}\label{final-element-modificat
 \end{nonnormative}
 
 \begin{example}
+Final component modification.
 \begin{lstlisting}[language=modelica]
 type Angle =
   Real(final quantity = "Angle", final unit = "rad", displayUnit = "deg");
@@ -570,6 +571,28 @@ \subsection{Final Element Modification Prevention}\label{final-element-modificat
 \end{lstlisting}
 \end{example}
 
+\begin{example}
+Final class declaration.
+\begin{lstlisting}[language=modelica]
+model Test2
+  final model MyTF = TransferFunction(b = {1, 2});
+  /* Equivalently:
+  final model MyTF = TransferFunction(final a, final b = {1, 2});
+  */
+  MyTF tf1;                        // fine
+  MyTF tf2(a = {1, 2});            // error, all elements in MyTF are final
+  model M = MyTF(a = {4});         // error, all elements in MyTF are final
+  model TFX
+    extends MyTF;                  // fine
+    Real foo = 1.0;
+  end TFX;
+  TFX tfx(foo = 2.0);              // fine, foo is not from MyRF
+  TFX tfx2(a = {1, 3});            // error, all elements from MyTF are final
+  model TFX3 = TFX(a = {1, 4});    // error, all elements from MyTF are final
+end Test2;
+\end{lstlisting}
+\end{example}
+
 \section{Redeclaration}\label{redeclaration}
 
 A \lstinline!redeclare! construct in a modifier replaces the declaration of a local class or component with another declaration.  A \lstinline!redeclare! construct as an element replaces the declaration of a local class or component with another declaration.  Both \lstinline!redeclare! constructs work in the same way.  The \lstinline!redeclare! construct as an element requires that the element is inherited, and cannot be combined with a modifier of the same element in the extends-clause.  For modifiers the redeclare of classes uses a special short-class-definition construct; that is a subset of normal class definitions and semantically behave as the corresponding class-definition.