public function replaceQuestionMark(
        /*# string */ $string,
        array $values
    )/*# : string */ {
        $pat = $rep = [];
        foreach ($values as $val) {
            $pat[] = '/\?/'; // question mark
            $rep[] = $this->getPlaceholder($val); // placeholder
        }
        return preg_replace($pat, $rep, $string, 1);
    }