Sentence linebreaks.

Add note that variability is differently defined for variables and expressions.

chapters/classes.tex

@@ -346,17 +346,12 @@ \subsection{Component Variability Prefixes discrete, parameter, constant}\label{
 \item
   A \emph{discrete-time} variable \lstinline!vd! is a variable declared with the \lstinline!discrete!\indexinline{discrete} prefix, or a variable without any prefix that is not a continuous-time variable.
   It has a vanishing time derivative between events.
-  Note that this is not the same as saying that \lstinline!der(vd)=0! almost everywhere,
-  as the derivative is not even defined at the events, and it is not legal
-  to apply \lstinline!der! to discrete-time variables as they are not continuous. 
+  Note that this is not the same as saying that \lstinline!der(vd)=0! almost everywhere, as the derivative is not even defined at the events, and it is not legal to apply \lstinline!der! to discrete-time variables as they are not continuous. 
   During transient analysis the variable can only change its value at event instants (see \cref{events-and-synchronization}).
 \item
-  A continuous-time variable is a \lstinline!Real! variable without any prefix that is not assigned in a \lstinline!when!-clause.
-  A \emph{continuous-time} variable \lstinline!vn! may have a non-vanishing time
-  derivative (\lstinline!der(vn)<>0! possible) and may also
-  change its value discontinuously at any time during transient analysis
-  (see \cref{events-and-synchronization}). If there are any discontinuities the variable is
-  not differentiable.
+  A \emph{continuous-time} variable is a \lstinline!Real! variable without any prefix that is not assigned in a \lstinline!when!-clause.
+  A continuous-time variable \lstinline!vn! may have a non-vanishing time derivative (\lstinline!der(vn)<>0! possible) and may also change its value discontinuously at any time during transient analysis (see \cref{events-and-synchronization}).
+  If there are any discontinuities the variable is not differentiable.
 \end{itemize}
 
 Components declared as \lstinline!constant! shall have an associated declaration equation with a constant expression, if the constant is directly in the simulation model, or used in the simulation model.
@@ -388,6 +383,9 @@ \subsection{Component Variability Prefixes discrete, parameter, constant}\label{
 definition equations is given in \cref{variability-of-expressions}.
 
 \begin{nonnormative}
+Note that for expressions discrete-time expressions include parameter expressions, whereas discrete-time variables do not include parameter variables.
+This is consistent with restrictions on variability for expressions normally being upper limits.
+
 For \lstinline!Real! variables we can distinguish two subtly different categories: discrete-time and piecewise constant, where the discrete-time variables are a subset of all piecewise constant variables.
 The \lstinline!Real! variables declared with the prefix \lstinline!discrete! is a subset of the discrete-time \lstinline!Real! variables.
 For a \lstinline!Real! variable, being discrete-time is equivalent to being assigned in a \lstinline!when!-clause.