use XML::Twig qw( );

# Assumptions
# - "data" elements can't be nested.
# - Only one twig instance is used at a time.

my $prune_data;

sub twig_data_start {
   my ($twig, $ele) = @_;
   $prune_data = 0;
   return 1;
}

sub twig_data_type {
   my ($twig, $ele) = @_;
   $prune_data = 1 if $ele->trimmed_text() eq 'yyy';
   return 1;
}

sub twig_data {
   my ($twig, $ele) = @_;
   return 1 if !$prune_data;
   $prune_data = 0;
   $ele->delete();
   return 0;
}

my $twig = XML::Twig->new(
   start_tag_handlers => {
      'data'      => \&twig_data_start,
   },

   twig_handlers => {
      'data'      => \&twig_data,
      'data/type' => \&twig_data_type,
   },

   # Output will be nicely formatted, but not necessarily valid.
   pretty_print => 'indented',
);

$twig->parse(\*DATA);
$twig->print();


__DATA__
<doc>
   <data>
      <type>xxx</type>
      <vars>a</vars>
   </data>
   <data>
      <type>yyy</type>
      <vars>b</vars>
   </data>
</doc>

##</code><code>##

<doc>
  <data>
    <type>xxx</type>
    <vars>a</vars>
  </data>
</doc>