sub get_list
{
    my ( $self, @capwords ) = @_;

    # return nothing in void context
    return unless defined wantarray;

    # return nothing if there are no items
    return unless $self->{items};

    # return filtered list in list context
    return grep { $_->is( @capwords ) } @{ $self->{items} } if wantarray;

    # return the first filtered element in scalar context
    for my $item ( @{ $self->{items} } )
    {
        return $item if $item->is( @capwords );
    }

    # explicitly return nothing if there's no filtered list
    return;
}