比如下面的例子，应该只列出2行内容，但是按照这个xml结构，就列出3个了。怎么办，谢谢。（其中，xxx,yyy,zzz不应该列出来）

<books>
  <book>
    <author name="hehe">Jack Herrington</author>
    <title>PHP Hacks</title>
    <publisher>O'Reilly</publisher>
  <book>
    <author>xxx</author>
    <title>yyy</title>
    <publisher>zzz</publisher>
  </book>    
  </book>
  <book>
    <author>Jack Herrington</author>
    <title>Podcasting Hacks</title>
    <publisher>O'Reilly</publisher>
  </book>
</books>

php代码：
<?php
  $doc = new DOMDocument();
  $doc->load( 'books.xml' );
  $books = $doc->getElementsByTagName( "book" );
  foreach( $books as $book )
  {
  $authors = $book->getElementsByTagName( "author" );
  $author = $authors->item(0)->nodeValue;
  $publishers = $book->getElementsByTagName( "publisher" );
  $publisher = $publishers->item(0)->nodeValue;
  $titles = $book->getElementsByTagName( "title" );
  $title = $titles->item(0)->nodeValue;
  echo "$title - $author - $publisher<br/>\n";
  }
  ?>