动态创建XML时出错

Question

I want to create an XML document of this type:

<?xml version="1.0" encoding="UTF-8"?>
<libreria version="1">
<libri>

</libri>
</libreria>

and then insert in various other fields like <libro><data></data></libro>.

I created the following code:

<?php
$note=<<<XML
<?xml version="1.0" encoding="UTF-8"?>
<libreria version="1">
</libreria>
XML;
$mioArray = new SimpleXMLElement($note); 
$result =$mioArray->addChild('libri');
$result2 = $result->addChild('libro');
$result2->addChild('data', 22);
echo $result2->asXML();
?>

But when print the output, I don't see the first part in this $notes . What am I doing wrong?