A question about reordering XML

[mtimofiiv]

Hi there, so here's my sample XML file:

<root>
<item number="1"/>
<item number="4"/>
<item number="2"/>
<item number="3"/>
</root>

I'm building a backend to edit some XML for a client out of PHP, and I need it to sort the items by the "number" attribute. I've tried a few methods, including arrays, but I seem to be having some trouble still. I can't use XSLT unfortunately on the server where this is heading.

I've played with the following code so far, but I seem to be having trouble saving it back into the XML file after.

    $url = '_db/items.xml';
    $file = simplexml_load_file($url);
    $sxe = new SimpleXMLElement($file->asXML());

    $nodes = $sxe->xpath('/root/item');

    function sort_items($t1, $t2) {
        return strcmp($t1['number'], $t2['number']);
    }

    usort($nodes, 'sort_items');
    $sxe->asXML($url); 

Any ideas?

[mtimofiiv]

Oh, and I forgot to mention.

var_dump($nodes); 

This returns an array with SimpleXMLElement objects in it. So maybe the problem is that it's in an array?