public function decrement($key, $offset = 1) {
		if ($this->_config['scope']) {
			$key = "{$this->_config['scope']}_{$key}";
		}
		if (!$result = $this->_read($key)) {
			return false;
		}
		if (!$this->_write($key, $result['value'] -= $offset, $result['expiry'])) {
			return false;
		}
		return $result['value'];
	}