Using namespaces on XML - php

Question

I need work with namespaces on XML from a code and do something with it. For instance:
<system:include file="./test.php" cache="true" />
That would be the final output of the content, but it is necessary to process the special tags (like the system:include) before send to client.
So I will get all elements of final output to search about namespaced tags or specific ones. The problem is that if I use DOMDocument and read like XML, I have some problems with namespaces declaration (Namespace prefix system on include is not defined in Entity).
My test code is:
<?php
$document = new DOMDocument();
$document->loadXML('
<system:include file="./test.php" cache="true" />
');
foreach($document->childNodes as $node) {
var_dump($node->nodeName);
}
?>
I need do it because I need process some special tags and converts it to real HTML. For instance: convert <b> to <strong> (just an example!) or make something better like include and cache a specific page using tags.
Another example:
<h7>Hello World!</h7>
Converts to:
<div class="h7">Hello World!</div>
Note: the ob contents will be sent to a specific method that will search by this special tags. So I don't know if I can make namespaces declaration before (will be hard and slowly, probably).
Bye!

Answer 1

I can get it to work if I specify a root element in the XML, and then declare the system namespace inside the root element. <root xmlns:system="system">...</root>
<?php
function dump($root) {
foreach($root->childNodes as $node) {
echo $node->nodeName;
echo "\n";
dump($node);
}
}
$doc = new DOMDocument();
$doc->loadXML('<root xmlns:system="system"><system:include file="./test.php" cache="true" /></root>');
dump($doc);
?>