Reference connector balancing restriction.

Closes modelica#3260

chapters/classes.tex

@@ -965,7 +965,7 @@ \section{Balanced Models}\label{balanced-models}
 \item
   The number of input and flow variables present in each (top-level) public connector component.
   \begin{nonnormative}
-  This represents the number of connection equations that will be provided when the class is used.
+  This represents the number of connection equations that will be provided when the class is used, due to the balancing restrictions for connectors, see \cref{balancing-restriction-and-size-of-connectors}.
   \end{nonnormative}
 \item
   The number of (top-level) public input variables that neither are connectors nor have binding equations.