my $sabal = new XML::Twig(        
              twig_roots          => {
                     'foo/yahoo'  =>
                     #'bayking[@id="kingtony"]'   =>
                         sub {  
                                my ($yabal, $element ) = @_;
                                if ( $element->first_child('bayking_list')->first_child('bayking')->att('id') eq 'kingtony' ) {
                                       $element->print;
                             }
                          }
              }
);

$sabal->parse($xml);