//创建DOMDocument
    $_doc = new DOMDocument();
    //载入XML文件
    $_doc->load('test.xml');
    //获取
    $_version = $_doc->getElementsByTagName('version');
    echo $_version->length;//3
    //item()表示第几个
    echo $_version->item(0)->nodeName; //version
    echo $_version->item(0)->nodeValue; // 1.0
    //遍历
    foreach ($_version as $_v){
        echo $_v->nodeValue;
    }

    //声明xml
    $_doc = new DOMDocument('1.0','utf-8');
    //排版格式
    $_doc->formatOutput = true;
    
    //创建内容
    $root = $_doc->createElement('root');
    $_doc->appendChild($root);
    $version = $_doc->createElement('version');
    $root->appendChild($version);
    $text = $_doc->createTextNode('1.0');
    $version->appendChild($text);
    
   //生成xml
   $_doc->save('test2.xml');