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 function 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 one of the following: a string (a function name), an indexed array of function names, or an associative array with keys being the function name and the associated value being the callable.

### Return Values

No value is returned.

### 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.

### Changelog

Version | Description
--- | ---
8.4.0 | Invalid callback names now throws a ValueError. Passing a non-callable entry now throws a TypeError.
8.4.0 | It is now possible to use callables for callbacks when using `restrict` with array entries.

### 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('examples/book-simple.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('examples/book-simple.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

Example #4 DOMXPath::registerPhpFunctions() with a callable

    <?php
    $doc = new DOMDocument;
    $doc->load('examples/book-simple.xml');

    $xpath = new DOMXPath($doc);

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

    // Register PHP functions (has_multiple only)
    $xpath->registerPhpFunctions(["has_multiple" => fn ($nodes) => 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
- XSLTProcessor::registerPHPFunctions() - Enables the ability to use PHP functions as XSLT functions

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