public function setPaperSize($sSize = null, $sOrientation = null)
    {
        $this->sPaperSize        = $sSize ?: static::DEFAULT_PAPER_SIZE;
        $this->sPaperOrientation = $sOrientation ?: static::DEFAULT_PAPER_ORIENTATION;
        $this->oDomPdf->setPaper($this->sPaperSize, $this->sPaperOrientation);
        return $this;
    }