function exists($key,&$val=NULL) {
		$fw=Base::instance();
		if (!$this->dsn)
			return FALSE;
		$ndx=$this->prefix.'.'.$key;
		$parts=explode('=',$this->dsn,2);
		switch ($parts[0]) {
			case 'apc':
			case 'apcu':
				$raw=call_user_func($parts[0].'_fetch',$ndx);
				break;
			case 'redis':
				$raw=$this->ref->get($ndx);
				break;
			case 'memcache':
				$raw=memcache_get($this->ref,$ndx);
				break;
			case 'memcached':
				$raw=$this->ref->get($ndx);
				break;
			case 'wincache':
				$raw=wincache_ucache_get($ndx);
				break;
			case 'xcache':
				$raw=xcache_get($ndx);
				break;
			case 'folder':
				$raw=$fw->read($parts[1].$ndx);
				break;
		}
		if (!empty($raw)) {
			list($val,$time,$ttl)=(array)$fw->unserialize($raw);
			if ($ttl===0 || $time+$ttl>microtime(TRUE))
				return [$time,$ttl];
			$val=null;
			$this->clear($key);
		}
		return FALSE;
	}