php simplexml 如何删除节点

<?php
//[需求]：删除所有书籍的year节点
$sxe = simplexml_load_file("bookstore.xml");
foreach ($sxe->book as $book) {
unset($book->year);  //删除year节点。删除变量用unset()。
}
 
$sxe->asXML(&#39;sxe_delete_book.xml&#39;);

<?xml version="1.0" encoding="utf-8" ?>
<bookstore>
    <book category="COOKING">
        <title>Everyday Italian</title>
        <author>Giada De Laurentiis</author>
        <year>2005</year>
        <price>30.00</price>
    </book>
    <book category="CHILDREN">
        <title>Harry Potter</title>
        <author>J K. Rowling</author>
        <year>2005</year>
        <price>29.99</price>
    </book>
    <book category="WEB">
        <title>Learning XML</title>
        <author>Erik T. Ray</author>
        <year>2003</year>
        <price>39.95</price>
    </book>
</bookstore>