$constraint =~ m@
	^\s*		# skip all whitespace at beginning
	(
		/.+/			# capture the custom regex
		|m(.).+\2	# does this capture the ops? What does the |m do? why is the (.) and \2 in there?
	)
	[cgimosx]*	# ?? don't understand what this is for. what are we trying to match? I thought the ops were matched above
	\s*$		# skip all whitespace at end
	@x

##</code><code>##

my $input = 'http://www.knowmad.com/';
my $constraint_good = '/[\\!@#%&_:\$\^\*\(\)\+\.\/]+/';
my $constraint_bad = '/[!@#%&_:\$\^\*\(\)\+\.\/]+\\/';


if ( $constraint_good =~ m@^\s*(/.+/|m(.).+\2)[cgimosx]*\s*$@ ) {
	my $sub = eval 'sub { $_[0] =~ '. $constraint_good .  '}';
		die "Error compiling regular expression $constraint_good: $@" if
			$@;
		print "matched\n";
} else {
	print "no good.\n"
}

if ( $constraint_bad =~ m@^\s*(/.+/|m(.).+\2)[cgimosx]*\s*$@ ) {
	my $sub = eval 'sub { $_[0] =~ '. $constraint_bad .  '}';
		die "Error compiling regular expression $constraint_bad:
			$@" if $@;
		print "matched\n";
} else {
	print "no good.\n"
}

##</code><code>##

matched
Error compiling regular expression /[!@#%&_:\$\^\*\(\)\+\.\/]+\/: Search pattern not terminated at (eval 2) line 1.