PHP: "Couldn't fetch DOMElement. Node no longer exists in" using DOMXpath - php

Question

I have some HTML that contains this:
<div class="test">
Outer
<div class="test">Inner 1</div>
<div class="test">Inner 2</div>
</div>
I'm doing str_replace() on the contents of these elements:
$dom = new DOMDocument();
$dom->loadHTML($html);
$xpath = new DOMXpath($dom);
foreach($xpath->query("//div[#class='test']") as $node) {
$node->nodeValue = str_replace(" ", "X", $node->nodeValue);
}
That should replace any spaces with an "X".
But it results in this error:
Warning: Couldn't fetch DOMElement. Node no longer exists in /path/to/my/file.php on line 63
It works if there's only one nested div:
<div class="test">
Outer
<div class="test">Inner 1</div>
</div>
Why does this happen, and how can I get it working?

Answer 1

Try changing
foreach($xpath->query("//div[#class='test']") as $node)
to
foreach($xpath->query('//div[#class="test"]//div[#class="test"]') as $node)
Edit per comments:
Assuming there's a space in the outer element (i.e., its "Outer 1:):
<?php
$string = <<<XML
<div class="test">
Outer 1
<div class="test">Inner 1</div>
<div class="test">Inner 2</div>
</div>
XML;
$dom = new DOMDocument();
$dom->loadHTML($string);
$xpath = new DOMXpath($dom);
foreach($xpath->query('//div[#class="test"]//text()') as $node) {
$nnode = trim($node->nodeValue);
echo $nnode = str_replace(" ", "X", $nnode);
}