修改和删除：

<?php
$doc=new DOMDocument();
$doc->load("php.xml");
$root=$doc->documentElement;

$books=$doc->getElementsByTagName("php100");
foreach ($books as $book) {
 if( $book->getAttribute('id')==2){
 echo $book->getAttribute('id')."-";
 echo $book->getElementsByTagName("index")->item(0)->nodeValue='test';
 echo "<br>";
 } 
 if($book->getAttribute('id')==4){
  $root->removeChild($book);
 }
}
$doc->save('php.xml');
?>

PHP生成XML文件

<?php

$doc=new DOMDocument('1.0', 'UTF-8');
$doc->formatOutput=true;
$php100=$doc->createElement_x('php100');

$php1000=$doc->createElement_x('php1000');

$php10000=$doc->createElement_x('title');

$php20000=$doc->createElement_x('content');

$val=$doc->createTextNode('333333333');

$val2=$doc->createTextNode('2222222222');

$val3=$doc->createTextNode('new');

$xmlnew=$doc->createAttribute('xmlnew');

$php20000->appendChild($val2);

$php10000->appendChild($val);

$php100->appendChild($php1000);

$php1000->appendChild($xmlnew);

$php1000->appendChild($php20000);

$php1000->appendChild($php10000);

$xmlnew->appendChild($val3);

$doc->appendChild($php100);

$doc->save('php.xml');

?>

<?xml version="1.0" encoding="UTF-8"?>
<php100>
  <php1000 xmlnew="new">
    <content>2222222222</content>
    <title>333333333</title>
  </php1000>
</php100>

PHP XML 的 DOMDocument 读取功能