Using a callback to fetch the current context in an xpath expression, this might allow to implement the CSS selector `:scope`

xpath-context.php

<?php

$xml = file_get_contents('php://stdin');

class MyXpath extends DOMXpath {

  private static $_context = null;
   
  public function __construct($document) {
    parent::__construct($document);
    $this->registerNamespace("php", "http://php.net/xpath");
    $this->registerPHPFunctions([self::CLASS.'::getContext']);
  }

  public function evaluate($expression, $context = NULL, $registerNamespaces = FALSE) {
    self::$_context = $context;
    return parent::evaluate($expression, $context, $registerNamespaces);
  }

  public function getContext() {
    return self::$_context;
  }
}

$document = new DOMDocument();
$document->loadXml($xml);
$xpath = new MyXpath($document);
$xpath->registerPhpFunctions(['getContext']);

foreach ($xpath->evaluate('//item') as $item) {
  var_dump($xpath->evaluate('name(//*/.)', $item));
  var_dump($xpath->evaluate('name(//*[. = php:function("MyXpath::getContext")])', $item));
}