

   DDrraaww aa vveerrttiiccaall lliinnee

        xline(x, ...)

   AArrgguummeennttss::

          x: Value on x axis specifying location of vertical
             line.

        ...: Any ploting options for abline function.

   EExxaammpplleess::

        plot(ozone$x[,2],ozone$y) # plot ozone longitude vs ozone value
        xline(42) # plots vertical line at longitude value of 42

