protected function makeTableHeader($caption)
    {
        if (is_array($caption)) {
            list($caption, $subcaption) = $caption;
        }

        $output = [];
        $output[] = '<tr>';
        $output[] = '<th colspan="3" colspan="100" style="'.$this->getHeaderCss().'">';
        $output[] = $caption;

        if (isset($subcaption)) {
            $output[] = '<div style="'.$this->getSubheaderCss().'">'.$subcaption.'</div>';
        }

        $output[] = '</td>';
        $output[] = '</tr>';
        return implode(PHP_EOL, $output);
    }