Register a PHP functions as namespaced XPath function

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- PHP Manual
- DOMXPath
- Register a PHP functions as namespaced XPath function

# DOMXPath::registerPhpFunctionNS

(PHP >= 8.4.0)

DOMXPath::registerPhpFunctionNS — Register a PHP functions as namespaced XPath function

### Description

public DOMXPath::registerPhpFunctionNS(string `$namespaceURI`, string `$name`, callable `$callable`): void

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

### 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.

### Errors/Exceptions

- Throws a ValueError if a callback name is not valid.
- Throws a ValueError if `options` contains an invalid option.
- Throws a ValueError if `overrideEncoding` is an unknown encoding.
- Throws a TypeError if a given callback is not callable.

### Return Values

No value is returned.

### Examples

Example #1 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";
    }

    ?>

The above example will output something similar to:

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

### See Also

- DOMXPath::registerNamespace() - Registers the namespace with the DOMXPath object
- DOMXPath::query() - Evaluates the given XPath expression
- DOMXPath::evaluate() - Evaluates the given XPath expression and returns a typed result if possible
- XSLTProcessor::registerPHPFunctions() - Enables the ability to use PHP functions as XSLT functions
- XSLTProcessor::registerPHPFunctionNS() - Register a PHP function as namespaced XSLT function