But Perl's m// operator is a more expressive grammar than formal regular expressions.
For example, \1 allows you to detect primes:
print "Prime" if (1 x shift) !~ /^1?$|^(11+?)\1+$/
And s/// can be used to detect balanced parenthesis:

$_ = '(()(()()))';
(my $re=$_)=~s/((\()|(\))|.)/${[')','']}[!$3]\Q$1\E${['(','']}[!$2]/gs
+;
eval{/$re/};
print "Balanced" unless $@ =~ /unmatched/;
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