use warnings;
use strict;

{
	package Foo;
	use warnings::register;
	sub bar {
		warnings::warnif("bar: $_[0]");
	}
}

{
	no warnings;
	Foo::bar("inside");
}
Foo::bar("outside");

use warnings::register;
use Carp;
{
	no warnings;
	warn "warn";
	warnings::warn("warnings::warn");
	carp "carp";
	warnings::warnif("inside 2");
}
warnings::warnif("outside 2");

__END__

bar: outside at w.pl line 17.
warn at w.pl line 23.
warnings::warn at w.pl line 24.
carp at w.pl line 25.

##</code><code>##

sub _debug {
	my ($self, $lvl, @out) = @_;
	return if $self->{debug}<$lvl || !@out;
	print STDERR __PACKAGE__, " DEBUG: ", @out, "\n";
}
# ...
$self->_debug(2, ...);