Clarify array range operator.

Closes modelica#3028

chapters/operatorsandexpressions.tex

@@ -105,10 +105,10 @@ \section{Operator Precedence and Associativity}\label{operator-precedence-and-as
 2-$\hspace{0pt}$-2 // = 4 in Mathematica/MATLAB; is illegal in Modelica
 \end{lstlisting}
 
-Non-associative exponentiation and array range operator:
+Non-associative exponentiation and array range operator (note that the array range operator only takes scalar operands):
 \begin{lstlisting}[language=modelica]
 x ^ y ^ z     // Not legal, use parentheses to make it clear.
-a : b : c : d // Not legal, and scalar arguments gives no legal interpretation.
+a : b : c : d // Not legal, and parentheses cannot make it legal.
 \end{lstlisting}
 \end{nonnormative}