c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'xyz1';
 ;;
 print '/\d \D/ matches'      if $s =~ m{ \d \D      }xms;
 print '/\d (?! \d)/ matches' if $s =~ m{ \d (?! \d) }xms;
"
/\d (?! \d)/ matches