Merge pull request #3439 from HansOlsson/NonIntegerUnitExponent

Support non-integer exponents to handle the result of square root

chapters/unitexpressions.tex

@@ -42,12 +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 ")" )
 \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! consists of a \lstinline[language=grammar]!unit-operand! possibly suffixed by a possibly signed integer number, which is interpreted as an exponent.
+A \lstinline[language=grammar]!unit-factor! consists of a \lstinline[language=grammar]!unit-operand! possibly suffixed by a possibly signed integer or rational number, which is interpreted as an exponent.
 There must be no spacing between the \lstinline[language=grammar]!unit-operand! and a possible \lstinline[language=grammar]!unit-exponent!.
+It is recommended to use the simplest representation of exponents, meaning that the explicit \lstinline!+! sign should be avoided, that leading zeros should be avoided, that rational exponents are reduced to not have common factors in the numerator and denominator, that rational exponents with denominator 1 should be avoided in favor of plain integer exponents, that the exponent 1 is omitted, and that entire factors with exponent 0 are omitted.
 
 \begin{lstlisting}[language=grammar]
 unit-operand :