логика кода на opencart 2

не могу понять логику кода из opencart 2, ...

class Request {
public $get = array();
public $post = array();
public $cookie = array();
public $files = array();
public $server = array();
public function __construct() {
    $this->get = $this->clean($_GET);
    $this->post = $this->clean($_POST);
    $this->request = $this->clean($_REQUEST);
    $this->cookie = $this->clean($_COOKIE);
    $this->files = $this->clean($_FILES);
    $this->server = $this->clean($_SERVER);
}
public function clean($data) {
    if (is_array($data)) {
        foreach ($data as $key => $value) {
            unset($data[$key]);
            $data[$this->clean($key)] = $this->clean($value);
        }
    } else {
        $data = htmlspecialchars($data, ENT_COMPAT, 'UTF-8');
    }
    return $data;
}
}

а точнее, этот кусок ...

public function clean($data) {
    if (is_array($data)) {
        foreach ($data as $key => $value) {
            unset($data[$key]);
            $data[$this->clean($key)] = $this->clean($value);
        }
    } else {
        $data = htmlspecialchars($data, ENT_COMPAT, 'UTF-8');
    }
    return $data;
}