PHP Manual: Register a PHP functions as namespaced XPath function

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.

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

DOMXPath::registerPhpFunctionNS

Description

Parameters

Errors/Exceptions

Return Values

Examples

See Also