Register PHP functions as XPath functions

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- Register PHP functions as XPath functions

# DOMXPath::registerPhpFunctions

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

DOMXPath::registerPhpFunctions — Register PHP functions as XPath functions

### Description

public DOMXPath::registerPhpFunctions(string|array|null `$restrict` = `null`): void

This method enables the ability to use PHP functions within XPath expressions.

### Parameters

`restrict`

  Use this parameter to only allow certain functions to be called from XPath.

  This parameter can be either a string (a function name) or an array of function names.

### Return Values

No value is returned.

### Examples

The following examples use book.xml which contains the following:

Example #1 book.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <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>

Example #2 DOMXPath::registerPHPFunctions() with `php:functionString`

    <?php$doc = new DOMDocument;$doc->load('book.xml');$xpath = new DOMXPath($doc);// Register the php: namespace (required)$xpath->registerNamespace("php", "http://php.net/xpath");// Register PHP functions (no restrictions)$xpath->registerPHPFunctions();// Call substr function on the book title$nodes = $xpath->query('//book[php:functionString("substr", title, 0, 3) = "PHP"]');echo "Found {$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

Example #3 DOMXPath::registerPHPFunctions() with `php:function`

    <?php$doc = new DOMDocument;$doc->load('book.xml');$xpath = new DOMXPath($doc);// Register the php: namespace (required)$xpath->registerNamespace("php", "http://php.net/xpath");// Register PHP functions (has_multiple only)$xpath->registerPHPFunctions("has_multiple"); function has_multiple($nodes) {    // Return true if more than one author    return count($nodes) > 1;}// Filter books with multiple authors$books = $xpath->query('//book[php:function("has_multiple", author)]');echo "Books with multiple authors:\n";foreach ($books as $book) {    echo $book->getElementsByTagName("title")->item(0)->nodeValue . "\n";}?>

The above example will output something similar to:

    Books with multiple authors:
    PHP Basics

### 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