public function get_margin_width()
    {
        $style = $this->_style;

        return (float)$style->length_in_pt(array(
            $style->width,
            $style->margin_left,
            $style->margin_right,
            $style->border_left_width,
            $style->border_right_width,
            $style->padding_left,
            $style->padding_right
        ), $this->_containing_block["w"]);
    }