public static function FILTER_SANITIZE_TURTLE_STRING($value)
	{
		$value = preg_replace('/\\\\/', '\\\\\\\\', $value);	// escape backslash
		$value = preg_replace('/\r?\n|\r/', '\\n', $value);  // newline 
		$value = preg_replace('/"/', '\\"', $value);		// escape double quote
		
		return $value?:null;
	}