Add non-normative paragraph about pretty-printing

chapters/operatorsandexpressions.tex

@@ -121,6 +121,14 @@ \section{Operator Precedence and Associativity}\label{operator-precedence-and-as
 \end{lstlisting}
 \end{nonnormative}
 
+\begin{nonnormative}
+The operator precedence table is useful when generating textual representations of Modelica expression trees.
+When doing this, attention must be paid to the rule that the unary additive operators are only allowed for the first term in a sum.
+A naive implementation might not produce all the required parentheses for an expression tree such as \lstinline!1 + (-1)!, as it might think that the higher precedence of the unary operator makes the parentheses redundant.
+A trick that solves this problem is to instead treat the additive unary operators as left associative with the same precedence as the binary additive operators.
+\end{nonnormative}
+
+
 \section{Evaluation Order}\label{evaluation-order}
 
 A tool is free to solve equations, reorder expressions and to not evaluate expressions if their values do not influence the result (e.g.\ short-circuit evaluation of \lstinline!Boolean! expressions).