XML分析错误 - 文档末尾的额外内容

Question

我一直在学习使用PHP创建XML页面的教程。以下是代码。

<?
header('Content-type: text/xml');

mysql_connect('localhost','root','admin');
mysql_select_db('test');

$sql = "Select * from `books`";
$q   = mysql_query($sql) or die(mysql_error());


$dom = new DOMDocument();

$datas = $dom->createElement('datas');
$dom->appendChild($datas);

while($r = mysql_fetch_array($q)){
  $id = $dom->createElement('id');
  $idText = $dom->createTextNode($r['id']);
  $id->appendChild($idText);

  $title = $dom->createElement('title');
  $titleText = $dom->createTextNode($r['title']);
  $title->appendChild($titleText);

  $author = $dom->createElement('author');
  $authorText = $dom->createTextNode($r['author']);
  $author->appendChild($authorText);

  $book = $dom->createElement('book');
  $book->appendChild($id);
  $book->appendChild($title);
  $book->appendChild($author);

  $datas->appendChild($book);

}


$xmlString = $dom->saveXML();
echo $xmlString;

?>

但由于某些原因，当我运行此操作时，我收到一个错误 - “第1行第5行的错误：文档末尾的额外内容”