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How can I find out the namespace of an element in PHP DOM?

Answer 1

+2 A:

With PHP 5.2.6 i've found 2 ways to this:

<?php
$xml = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?'.
       '><html xmlns="http://www.w3.org/1999/xhtml" lang="en"></html>';
$x = DomDocument::loadXml($xml);
var_dump($x->documentElement->getAttribute("xmlns"));
var_dump($x->documentElement->lookupNamespaceURI(NULL));

prints

string(28) "http://www.w3.org/1999/xhtml"
string(28) "http://www.w3.org/1999/xhtml"

Hope thats what you asked for :)

edorian 2010-08-25 14:19:12

Thanks for your answer - it doesn't solve my problem but tips me off that it seems to be something peculiar to documents loaded in from loadHTML() rather than loadXML() because indeed, your example works with loadXML(). Looks like loadHTML creates documents with an "invisible namespace" which can't be read using DOM methods but which appears when you saveXML().

thomasrutter 2010-08-25 14:26:06

I'm not sure i can follow you 100% but loading something with loadHtml and resaving it via saveXml doesnt add a xmlns for me. It just adds / preserves a doctype from the html. Maybe if you can provide a little reproduce script alongside the output you want i can dig deeper

edorian 2010-08-25 14:33:43

Interesting - it sometimes does and sometimes doesn't. If your input HTML document has an XHTML DOCTYPE, it does. It will do it for this input: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

thomasrutter 2010-09-29 03:22:13

I have NO idea how you would detect that in a DOM.

thomasrutter 2010-09-29 03:22:43

Answer 2

+1 A:

Well, you can do so with a function like this:

function getNamespaces(DomNode $node, $recurse = false) {
    $namespaces = array();
    if ($node->namespaceURI) {
        $namespaces[] = $node->namespaceURI;
    }
    if ($node instanceof DomElement && $node->hasAttribute('xmlns')) {
        $namespaces[] = $xmlns = $node->getAttribute('xmlns');
        foreach ($node->attributes as $attr) {
            if ($attr->namespaceURI == $xmlns) {
                $namespaces[] = $attr->value;
                }
        }
    }
    if ($recurse && $node instanceof DomElement) {
        foreach ($node->childNodes as $child) {
            $namespaces = array_merge($namespaces, getNamespaces($child, vtrue));
        }
    }
    return array_unique($namespaces);
}

So, you feed it a DomEelement, and then it finds all related namespaces:

$xml = '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <html xmlns="http://www.w3.org/1999/xhtml" 
         lang="en" 
         xmlns:foo="http://example.com/bar"&gt;
           <body>
                <h1>foo</h1>
                <foo:h2>bar</foo:h2>
           </body>
 </html>';
var_dump(getNamespaces($dom->documentElement, true));

Prints out:

array(2) {
  [0]=>
  string(28) "http://www.w3.org/1999/xhtml"
  [3]=>
  string(22) "http://example.com/bar"
}

Note that DomDocument will automatically strip out all unused namespaces...

As for why $dom->documentElement->namespaceURI is always null, it's because the document element doesn't have a namespace. The xmlns attribute provides a default namespace for the document, but it doesn't endow the html tag with a namespace (for purposes of DOM interaction). You can try doing a $dom->documentElement->removeAttribute('xmlns'), but I'm not 100% sure if it will work...

ircmaxell 2010-08-25 14:34:55

Answer 3

+3 A:

Like edorian already showed, getting the namespace works fine when the Markup is loaded with loadXML. But you are right that this wont work for Markup loaded with loadHTML:

$html = <<< XML
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:m="foo" lang="en">
    <body xmlns="foo">Bar</body>
</html>
XML;

$dom = new DOMDocument;
$dom->loadHTML($html);

var_dump($dom->documentElement->getAttribute("xmlns"));
var_dump($dom->documentElement->lookupNamespaceURI(NULL));
var_dump($dom->documentElement->namespaceURI);

will produce empty results. But you can use XPath

$xp = new DOMXPath($dom);
echo $xp->evaluate('string(@xmlns)');
// http://www.w3.org/1999/xhtml;

and for body

echo $xp->evaluate('string(body/@xmlns)'); // foo

or with context node

$body = $dom->documentElement->childNodes->item(0);
echo $xp->evaluate('string(@xmlns)', $body);
// foo

My uneducated assumption is that internally, a HTML Document is different from a real Document. Internally libxml uses a different module to parse HTML and the DOMDocument itself will be of a different nodeType, as you can simply verify by doing

var_dump($dom->nodeType); // 13 with loadHTML, 9 with loadXml

with 13 being a XML_HTML_DOCUMENT_NODE.

Gordon 2010-08-25 14:36:12

very nice and detailed, didn't know about the nodeTypes depending on the parsing method but it makes sense

edorian 2010-08-25 15:31:24

Thanks for the hint about nodetypes and the ability to use xpath - solves lots of my problems!

thomasrutter 2010-08-26 04:12:17

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How can I find out the namespace of an element in PHP DOM?

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