=head2 SYNOPSIS

 ...

 $node->climb_up(sub {
    my ($ancestor, $onTop_return) = @_;
    my $ret = $ancestor->doSomething();
    return if $ret->smells(); # climb_up immediately returns ()
    return do_whatever_with($ret); # i.e. any return values untouched
    $onTop_return->(@ignore_if_not); # Don't forget at the end!
        # otherwise ancestors' line processed ends by the parent
        # (blame perl it'd enforce an implied C<return @last_expr_val;> )
 }