file - Project\Client.pm

package Project::Client;
use strict;

sub new
{
	my ($class, %args) = shift;
	$class = ref ($class) || $class;

	my $self = {};
	
	...
		
	bless ($self, $class);
	return $self;
}

...

file - Project\Client\Mode.pm

package Project::Client::Mode;
@ISA = ('Project::Client');
use strict;

...

file - Project\Client\Mode\TestMode.pm

package Project::Client::Mode::TestMode;
@ISA = ('Project::Client::Mode');
use strict;

...


##</code><code>##


file - client.pl

use strict;
use lib '...';

my $mode = Project::Client::Mode::TestMode -> new (...);

...