public function allNumberFormats(PHPExcel $pPHPExcel = null)
    {
        // Get an array of unique number formats
        $aNumFmts = array();
        $aStyles = $this->allStyles($pPHPExcel);

        foreach ($aStyles as $style) {
            if ($style->getNumberFormat()->getBuiltInFormatCode() === false && !array_key_exists($style->getNumberFormat()->getHashCode(), $aNumFmts)) {
                $aNumFmts[ $style->getNumberFormat()->getHashCode() ] = $style->getNumberFormat();
            }
        }

        return $aNumFmts;
    }