use warnings; use strict;
use Encode;
use XML::Twig;
binmode STDERR, ":encoding(iso-8859-2)";
our(@XMLH, @xmln, @tw, @pa, @eof, @it, $two, $roo);
for my $n (0 .. 1) {
	$xmln[$n] = shift || ("a1.xml", "a2.xml")[$n];
	open $XMLH[$n], "<", $xmln[$n] or die "error open xml${n}: $!";
	$tw[$n] = XML::Twig->new;
	$tw[$n]->setTwigHandler("item", sub {
		my($twt, $e) = @_;
		my $t = $e->text;
		#warn " "x(24+8*$n), "${n}g|$t|\n";
		push @{$it[$n]}, $t;
		$twt->purge;
	});
	$pa[$n] = $tw[$n]->parse_start;
	$it[$n] = [];
}
$two = XML::Twig->new(output_filter => "safe", pretty_print => "nice");
$roo = XML::Twig::Elt->new("doc");
$two->set_root($roo);
while (1) {
	my $n = undef; my $itq = 1e9999;
	for my $j (0 .. 1) {
		if (!$eof[$j] && @{$it[$j]} <= $itq) {
			$n = $j; $itq = @{$it[$j]};
		}
	}
	if (!defined($n)) {
		last;
	}
	if (read $XMLH[$n], my $b, 20) {
		#my $bp = decode("iso-8859-2", $b); $bp =~ y/\r\n/./;
		#warn " "x(8+8*$n), "${n}r|$bp|\n";
		$pa[$n]->parse_more($b);
	} else {
		eof($XMLH[$n]) or die "error reading xml${n}";
		$pa[$n]->parse_done;
		$eof[$n]++;
	}
	my $eo;
	while (@{$it[0]} && @{$it[1]}) {
		my $i0 = shift @{$it[0]};
		my $i1 = shift @{$it[1]};
		$eo = XML::Twig::Elt->new("item", "$i0 $i1");
		$eo->paste_last_child($roo);
		#warn "p|$i0 $i1|\n";
	}
	if (defined($eo)) {
		$two->flush_up_to($eo);
	}
}
for my $n (0 .. 1) {
	if (my $c = @{$it[$n]}) {
		warn "warning: xml${n} has $c additional items";
	}
}
$two->flush;
#warn "all done";
__END__