PHP | DOMXPath registerPhpFunctions() Function

The DOMXPath::registerPhpFunctions() function is an inbuilt function in PHP which is used to enable the ability to use PHP functions within XPath expressions.

Syntax:

void DOMXPath::registerPhpFunctions( mixed $restrict )

Parameters: This function accepts an optional single parameter $restrict which holds the function to restrict.

Return Value: This function does not return any value.

Below given programs illustrate the DOMXPath::registerPhpFunctions() function in PHP:

Program 1:

<?php

// Create a new DOMDocument instance
$document = new DOMDocument();

// Create a XML
$xml = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<books>
    <book>
        <title>FOO BAR</title>
        <author>Mr. A</author>
        <author>Mr. B</author>
    </book>
    <book>
        <title>FOO BAZ</title>
        <author>Mr. C</author>
    </book>
</books>
XML;

// Load the XML
$document->loadXML($xml);

// Create a new DOMXPath instance
$xpath = new DOMXPath($document);

// Register the php: namespace
$xpath->registerNamespace("php",
        "http://php.net/xpath");

// Register PHP functions
$xpath->registerPHPFunctions();

// Use the PHP function to find
// the books starting with FOO
$query = '//book[php:functionString('
        . '"substr", title, 0, 3) = "FOO"]';

// Execute the query
$entries = $xpath->evaluate($query);

echo "Found $entries->length books"
        . " starting with 'FOO':\n";
foreach ($entries as $node) {
    $title = $node->getElementsByTagName(
                "title")->item(0)->nodeValue;
    echo "<br>$title";
}
?>

Output:

Found 2 books starting with 'FOO':
FOO BAR
FOO BAZ

Program 2:

<?php

// Create a new DOMDocument instance
$document = new DOMDocument();

// Create a XML
$xml = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<books>
    <book>
        <title>FOO BAR</title>
        <author>Mr. A</author>
        <author>Mr. B</author>
    </book>
    <book>
        <title>FOO BAZ</title>
        <author>Mr. C</author>
    </book>
</books>
XML;

// Load the XML
$document->loadXML($xml);

// Create a new DOMXPath instance
$xpath = new DOMXPath($document);

// Register the php: namespace
$xpath->registerNamespace("php",
        "http://php.net/xpath");

// Register PHP functions
$xpath->registerPHPFunctions();

// Use the manually created
// PHP function in query
$query = '//book[php:function('
        . '"has_multiple", author)]';

// Execute the query
$entries = $xpath->evaluate($query);

echo "Found $entries->length books "
        . "with multiple authors:\n";

foreach ($entries as $node) {
    $title = $node->getElementsByTagName(
            "title")->item(0)->nodeValue;
    echo "<br>$title";
}

function has_multiple($nodes) {

    // Return true if more than
    // one author is there
    return count($nodes) > 1;
}
?>

Output:

Found 1 books with multiple authors:
FOO BAR

Reference: https://www.php.net/manual/en/domxpath.registerphpfunctions.php