public function add($key, $amount) {
			if (!$this->allowed($key))
				throw new OutOfBoundsException(sprintf('"%s" is not an allowed key in strict mode', $key));
			else if (!$this->has($key))
				$this->counts->put($key, 0);

			$this->counts->put($key, $this->counts->get($key) + $amount);

			return $this->counts->get($key);
		}