sub gp_ref_date {
    my $self = shift;
    if(@_) { # setting
        my $date = shift;
        if($date =~ m! (\d+) / (\d+) (?:/ (\d+) )+!x) {
            my $y = $3;
            $y += ($y < 70) ? 2000 : 1900 if($y < 100);
            $date = sprintf "%4d-%02d-%02d", $y,$2,$1;
        }
        return $self->_gp_ref_date_accessor($date);
    } else {
        my $date = $self->_gp_ref_date_accessor(@_);
        $date =~ s!(\d{4})-(\d\d)-(\d\d)!$3/$2/$1!;
        return $date;
    }
}