public function combine() {

		$fieldnames = func_get_args();
		$values 	= [];

		foreach($fieldnames as $fieldname) {

			if(false === is_string($fieldname)) {
				return trigger_error(sprintf('All fieldnames used in "%s"() must be of the type string, "%s" given', __METHOD__, gettype($fieldname)), E_USER_ERROR);
			}

			$values[] = $this -> getValue($fieldname, $this -> getPrefix());
		}

		$combine = new Combine();
		$combine -> setValues($values);
		$combine -> setFieldnames($fieldnames);

		$this -> combine[] = $combine;

		return $combine;
	}