ad numeric options

Author: Vladimir Kotal

intro.tex

@@ -2084,7 +2084,9 @@
 should be lower case, 2--9 characters long and using only characters from
 the portable character set. Arguments without options should be possible to group
 after '--', etc.
-\item Using numbers of options is old fashioned; reportedly SUSv3 mentions that.
+\item Using numbers for options (ala \texttt{-4} and \texttt{-6} for some
+\texttt{ping} implementations) is old fashioned;
+reportedly SUSv3 mentions that.
 \item Watch out for GNU command line utilities and its strange permutations
 of options and arguments.
 \item The \texttt{-W} option should be reserved for vendor options, i.e. for