DOMXPath::registerPhpFunctionNS

Register a PHP functions as namespaced XPath function

&reftitle.description; public `void` `DOMXPath::registerPhpFunctionNS` `string` `namespaceURI` `string` `name` `callable` `callable`

This method enables the ability to use a PHP function as a namespaced XPath function inside XPath expressions.

&reftitle.parameters;

`namespaceURI`

- The URI of the namespace.

`name`

- The local function name inside the namespace.

`callable`

- The PHP function to call when the XPath function gets called within the XPath expression. When a node list is passed as parameter to the callback, they are arrays containing the matched DOM nodes.

&reftitle.returnvalues;

&return.void;

&reftitle.examples;

### Register a namespaced XPath function and call it from the XPath expression

    <?php

    $xml = <<<EOB
    <books>
    <book>
     <title>PHP Basics</title>
     <author>Jim Smith</author>
     <author>Jane Smith</author>
    </book>
    <book>
     <title>PHP Secrets</title>
     <author>Jenny Smythe</author>
    </book>
    <book>
     <title>XML basics</title>
     <author>Joe Black</author>
    </book>
    </books>
    EOB;

    $doc = new DOMDocument();
    $doc->loadXML($xml);

    $xpath = new DOMXPath($doc);

    // Register the my: namespace (required)
    $xpath->registerNamespace("my", "urn:my.ns");

    // Register PHP function
    $xpath->registerPHPFunctionNS(
        'urn:my.ns',
        'substring',
        fn (array $arg1, int $start, int $length) => substr($arg1[0]->textContent, $start, $length)
    );

    // Call substr function on the book title
    $nodes = $xpath->query('//book[my:substring(title, 0, 3) = "PHP"]');

    echo "Found {$nodes->length} books starting with 'PHP':\n";
    foreach ($nodes as $node) {
       $title  = $node->getElementsByTagName("title")->item(0)->nodeValue;
       $author = $node->getElementsByTagName("author")->item(0)->nodeValue;
       echo "$title by $author\n";
    }

    ?>

&example.outputs.similar;

    Found 2 books starting with 'PHP':
    PHP Basics by Jim Smith
    PHP Secrets by Jenny Smythe

&reftitle.seealso;

- `DOMXPath::registerNamespace`
- `DOMXPath::query`
- `DOMXPath::evaluate`
- `XSLTProcessor::registerPHPFunctions`
- `XSLTProcessor::registerPHPFunctionNS`