private function get_line_style($line)
    {
        //$style = null;
        $style = null;
        if (isset($this->highlight_extra_lines_styles[$line])) {
            $style = $this->highlight_extra_lines_styles[$line];
        }
        else { // if no "extra" style assigned
            $style = $this->highlight_extra_lines_style;
        }

        return $style;
    }