php echo xml documents with header

PHP Snippet 1:

<?php header("Content-type: text/xml"); ?>
<?php
    $xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";

PHP Snippet 2:

<?php 
    header("Content-type: text/xml"); 
    $xml="<?xml version=\"1.0\" encoding=\"UTF-8\"?>";

PHP Snippet 3:

echo '';print_r($output);echo '';die;