Register PHP functions as XPath functions
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    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