使用PHP DOMDocument替换XML节点的非文本

I want to replace innertext of a XML node my XML file named test.xml is

<?xml version="1.0" encoding="utf-8"?>
<ads>
    <loop>no</loop>
    <item>
        <description>Description 1</description>
    </item>
    <item>
        <description>Text in item2</description>
    </item>
    <item>
        <description>Let play with this XML</description>
    </item>
</ads>

I want to change the value of loop and description tag both, and it should be saved in test.xml like:

<?xml version="1.0" encoding="utf-8"?>
<ads>
    <loop>yes</loop>
    <item>
        <description>Description Changing Here</description>
    </item>
    <item>
        <description>Changing text in item2</description>
    </item>
    <item>
        <description>We will play later</description>
    </item>
</ads>

I tried code in PHP:

<?
    $file = "test.xml";
    $fp = fopen($file, "rb") or die("cannot open file");
    $str = fread($fp, filesize($file));
    $dom=new DOMDocument();
    $dom->formatOutput = true;
    $dom->preserveWhiteSpace = false;
    $dom->loadXML($str) or die("Error");
    //$dom->load("items.xml");

    $root=$dom->documentElement; // This can differ (I am not sure, it can be only documentElement or documentElement->firstChild or only firstChild)

    $loop=$root->getElementsByTagName('loop')->item(0);//->textContent;
    //echo $loop;
    if(trim($loop->textContent)=='no')
    {
        echo 'ok';
        $root->getElementsByTagName('loop')->item(0)->nodeValue ='yes';
    }
    echo "<xmp>NEW:
". $dom->saveXML() ."</xmp>";
?>

I tried only for loop tag.I don't know how to replace nodevalue in description tag. When I run this page it shows output like:

ok
NEW:
<?xml version="1.0" encoding="utf-8"?>
<ads>
    <loop>yes</loop>
    <item>
        <description>Description 1</description>
    </item>
    <item>
        <description>Changing text in item2</description>
    </item>
    <item>
        <description>Let play with this XML</description>
    </item>
</ads>

It gives the value yes in browser but don't save it in test.xml any reason?

So, since you have created DOMDocument you can use DOMXpath. Or keep using getElementsByTagName()

You could do this (but only in that context):

$descriptions = $root->getElementsByTagName('description');
foreach($descriptions as $nodeDesciption)
{
    $nodeDesciption->nodeValue ='Your custom value';
}