use strict;
use XML::Parser;
use XML::Writer;

my $writer = XML::Writer->new();
my $parser = XML::Parser->new(
   Handlers => {
      Init  => \&handle_Init,
      Start => \&handle_Start,
      Char  => \&handle_Char,
      End   => \&handle_End,
      Final => \&handle_Final,
   }
);

my $data  = do {local $/;<DATA>};

$parser->{match} = 'opponent';
$parser->parse($data);

sub handle_Init {
   $writer->xmlDecl('UTF-8');
   $writer->doctype('xml');
}

sub handle_Start {
   my($self,$name,%atts) = @_;
   $self->{flag} = 1 if $name eq $self->{match};
   $writer->startTag($name,%atts);
}

sub handle_Char {
   my($self,$text) = @_;
   if ($self->{flag}) {
      if ($text eq 'Terrance Rattigan') {
         $text = 'breakfast';
      }
      else {
         $text =~ s/goose/Queen Elizabeth/;
      }
      delete $self->{flag};
   }
   $writer->characters($text);
}

sub handle_End {
   my($self,$name) = @_;
   $writer->endTag($name);
}

sub handle_Final {
   $writer->end();
}

__DATA__
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xml>
<xml>
  <struggle class="life or death">
    <opponent>wolf</opponent>
    <opponent>ant</opponent>
  </struggle>
  <struggle class="life or death">
    <opponent>pantomime goose</opponent>
    <opponent>Terrance Rattigan</opponent>
  </struggle>
</xml>