use strict;
use warnings;
use XML::Twig;

my $xml = <<XML;
<doc>
   <data>
      <type>xxx</type>
      <vars>a</vars>
   </data>
   <data>
      <type>yyy</type>
      <vars>b</vars>
   </data>
</doc>
XML

my $root = XML::Twig->new (twig_handlers => {data => \&handler});

$root->parse ($xml);


sub handler {
    my $elt = $_;
    return if $elt->children (\&badType);

    print "Handling ", $elt->text (), "\n";
}


sub badType {
    return $_->text () =~ /^yyy/;
}