src/core/Request.php
public function isAjax(): bool
    {
        $param = $this->getServerParam('HTTP_X_REQUESTED_WITH', \FILTER_SANITIZE_STRING);
        return !is_null($param) && strtolower($param) === 'xmlhttprequest';
    }
public function isAjax(): bool
    {
        $param = $this->getServerParam('HTTP_X_REQUESTED_WITH', \FILTER_SANITIZE_STRING);
        return !is_null($param) && strtolower($param) === 'xmlhttprequest';
    }
It checks if the request is an ajax request.
@return boolean.