public function noticeErrors(string $heading, array $error_messages): string
    {
        if (!$error_messages) {
            return ''; // No errors.
        }
        $markup  = ''; // Initialize markup.
        $heading = $heading && mb_strpos($heading, '</i>') === false
            ? '<i class="sharkicon sharkicon-enty-exclamation"></i> '.$heading : $heading;
        $error_messages = $this->c::markdown($error_messages, ['no_p' => true]);

        if ($heading) { // Optional.
            $markup .= '<h3>'.$heading.'</h3>';
        }
        $markup .= '<ul><li>'.implode('</li><li>', $error_messages).'</li></ul>';

        return $markup;
    }