update to reflect the new significance of the "@" character

Doc/ref/ref2.tex

@@ -679,7 +679,7 @@ The following tokens serve as delimiters in the grammar:
 \index{delimiters}
 
 \begin{verbatim}
-(       )       [       ]       {       }
+(       )       [       ]       {       }      @
 ,       :       .       `       =       ;
 +=      -=      *=      /=      //=     %=
 &=      |=      ^=      >>=     <<=     **=
@@ -703,5 +703,5 @@ error:
 \index{ASCII@\ASCII}
 
 \begin{verbatim}
-@       $       ?
+$       ?
 \end{verbatim}