'1\b2'

##</code><code>##

       (??{
           local $N;
           ($N = $^N) =~ s/\w+//g; 
           (lc $N eq reverse lc $N)
             ? '' : (?!)
        })

##</code><code>##

       (??{
           local $N;
           ($N = $^N) =~ s/\w+//g; 
           (?!) if (lc $N ne reverse lc $N)
        })