protected function getStyleCss(array $tag_frag, $test_for_css = true)
    {
        if (empty($tag_frag['style_css'])) {
            return ''; // Not possible; no CSS code.
        }
        if ($test_for_css && !$this->isStyleTagFragCss($tag_frag)) {
            return ''; // This tag does not contain CSS.
        }
        return trim($tag_frag['style_css']); // CSS code.
    }