use warnings;
use strict;
use Mojo::DOM;

my $html = "<h1>a</h1>\n<p>b</p>\n<h2>c</h2>\n<p>d</p>\n"
	."<h3>e</h3>\n<p>f</p>\n<h2>g</h2>\n<p>h</p>\n<h2>i</h2>\n"
	."<h1>j</h1>\n<h2>k</h2>\n";
my $dom = Mojo::DOM->new($html);
$dom->find('h2')->each(sub {
	my $next = $_->next;
	my $new = $_->wrap('<div></div>');
	if ( $next && !$next->matches('h1') ) {
		$new->append($next);
		$next->remove;
	}
});
print "$dom";