Update according to decision.

Allow non-simplified fractions, but still prohibit m(4/2).

chapters/unitexpressions.tex

@@ -42,15 +42,13 @@ \section{The Syntax of Unit Expressions}\label{the-syntax-of-unit-expressions}
   unit-operand [ unit-exponent ]
 
 unit-exponent :
-   [ "+" | "-" ] UNSIGNED-INTEGER
-   | "^" "(" [ "+" | "-" ] UNSIGNED-INTEGER "/" UNSIGNED-INTEGER ")"
+   [ "+" | "-" ] ( UNSIGNED-INTEGER | "(" UNSIGNED-INTEGER "/" UNSIGNED-INTEGER ")" )
 \end{lstlisting}
 
 The SI standard uses super-script for the exponentation, and does thus not define any operator symbol for exponentiation.
 A \lstinline[language=grammar]!unit-factor! normally consists of a \lstinline[language=grammar]!unit-operand! possibly suffixed by a possibly signed integer number, which is interpreted as an exponent.
-Non-integer exponents are needed to fully support the unit for square roots (and can be used for roots in general).
-They are intended to be only be used when needed, and thus the fraction must be simplified and the denominator may not be one (or zero).
-They use an explicit exponentation operator to be easy to recognize.
+Rational exponents are needed to fully support the unit for square roots (and can be used for roots in general).
+They are intended to be only be used when needed, i.e., not to represent integer exponents.
 There must be no spacing between the \lstinline[language=grammar]!unit-operand! and a possible \lstinline[language=grammar]!unit-exponent!.
 
 \begin{lstlisting}[language=grammar]