protected function _duplicateBorder(&$val)
    {
        // 1 value => L => RTB
        if (count($val)==1) {
            $val[1] = $val[0];
            $val[2] = $val[0];
            $val[3] = $val[0];
        // 2 values => L => R & T => B
        } else if (count($val)==2) {
            $val[2] = $val[0];
            $val[3] = $val[1];
        // 3 values => T => B
        } else if (count($val)==3) {
            $val[3] = $val[1];
        }
    }