public static function check($mode)
    {
        $returnValue = (bool) false;
        
    	if (!is_string($mode)){
			throw new InvalidArgumentException('Try to check an irregular mode. The mode must be a string, ' . gettype($mode) . ' given.');
		}
    	else if (empty($mode)){
    		throw new InvalidArgumentException('Cannot check an empty mode.');
    	}
    	
    	$returnValue = in_array($mode, self::$current);

        return (bool) $returnValue;
    }