Align duplicated parts of lexing rules

This isn't the first time we have issues with these being out of sync.  Hopefully, maintenance will become easier now with the duplicated part being a substring of the full lexing rules.

chapters/lexicalstructure.tex

@@ -73,13 +73,17 @@ \subsection{Identifiers}\label{identifiers}
 The redundant escapes (\lstinline!'\?'! and \lstinline!'\"'!) are the same as the corresponding non-escaped variants (\lstinline!'?'! and \lstinline!'"'!), but are only for use in Modelica source code.
 A full BNF definition of the Modelica syntax and lexical units is available in \cref{modelica-concrete-syntax}.
 
+% For easy maintenance, the lexing rules below should be a substring of the full lexing rules in \cref{lexical-conventions}.
 \begin{lstlisting}[language=grammar]
-IDENT   = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
+IDENT = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
 Q-IDENT = "'" { Q-CHAR | S-ESCAPE } "'"
 NONDIGIT = "_" | letters "a" $\ldots$ "z" | letters "A" $\ldots$ "Z"
-DIGIT    = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
-Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$\mbox{\textdollar}$" | "%" | "&" | "(" | ")" | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "=" | "?" | "@" | "[" | "]" | "^" | "{" | "}"  | "|" | "~" | " " | """
-S-ESCAPE = "\'" | "\"" | "\?" | "\\" | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
+DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
+Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$\mbox{\textdollar}$" | "%" | "&" | "(" | ")"
+   | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "="
+   | "?" | "@" | "[" | "]" | "^" | "{" | "}" | "|" | "~" | " " | """
+S-ESCAPE = "\'" | "\"" | "\?" | "\\"
+   | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
 \end{lstlisting}
 
 \subsection{Names}\label{names}

chapters/syntax.tex

@@ -12,18 +12,19 @@ \section{Lexical conventions}\label{lexical-conventions}
 The following lexical units are defined (the ones in boldface are the
 ones used in the grammar, the rest are just internal to the definition
 of other lexical units):
+% Beware that the first lines of the lexing rules below are duplicated in \cref{identifiers}, and must be kept in sync.
 \begin{lstlisting}[language=grammar]
 IDENT = NONDIGIT { DIGIT | NONDIGIT } | Q-IDENT
 Q-IDENT = "'" { Q-CHAR | S-ESCAPE } "'"
 NONDIGIT = "_" | letters "a" $\ldots$ "z" | letters "A" $\ldots$ "Z"
-STRING = """ { S-CHAR | S-ESCAPE } """
-S-CHAR = see below
+DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 Q-CHAR = NONDIGIT | DIGIT | "!" | "#" | "$\mbox{\textdollar}$" | "%" | "&" | "(" | ")"
    | "*" | "+" | "," | "-" | "." | "/" | ":" | ";" | "<" | ">" | "="
    | "?" | "@" | "[" | "]" | "^" | "{" | "}" | "|" | "~" | " " | """
 S-ESCAPE = "\'" | "\"" | "\?" | "\\"
    | "\a" | "\b" | "\f" | "\n" | "\r" | "\t" | "\v"
-DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
+STRING = """ { S-CHAR | S-ESCAPE } """
+S-CHAR = see below
 UNSIGNED-INTEGER = DIGIT { DIGIT }
 UNSIGNED-REAL =
    UNSIGNED-INTEGER  "." [ UNSIGNED-INTEGER ]