function get_margin_height()
    {
        // This function is called in add_frame_to_line() and is used to
        // determine the line height, so we actually want to return the
        // 'line-height' property, not the actual margin box
        $style = $this->get_parent()->get_style();
        $font = $style->font_family;
        $size = $style->font_size;

        /*
        Helpers::pre_r('-----');
        Helpers::pre_r($style->line_height);
        Helpers::pre_r($style->font_size);
        Helpers::pre_r($this->_dompdf->getFontMetrics()->getFontHeight($font, $size));
        Helpers::pre_r(($style->line_height / $size) * $this->_dompdf->getFontMetrics()->getFontHeight($font, $size));
        */

        return ($style->line_height / ($size > 0 ? $size : 1)) * $this->_dompdf->getFontMetrics()->getFontHeight($font, $size);
    }