public function derivedValues($s) {
		preg_match_all('/@(\w+)/', $s, $possibilities, PREG_SET_ORDER);
		foreach ($possibilities as $possibility) {
			if ($this->offsetExists($possibility[1]) && is_string($this->offsetGet($possibility[1]))) {
				$s = str_replace($possibility[0], $this->offsetGet($possibility[1]), $s);
			}
		}
		return $s;
	}