static function retrieve($keys, $subtreeExpiry, $ttl, $useGlobalExpiry = true)
 {
     $keys = (array) $keys;
     self::filterKeys($keys);
     $nodeID = $subtreeExpiry ? eZTemplateCacheBlock::decodeNodeID($subtreeExpiry) : false;
     $cachePath = eZTemplateCacheBlock::cachePath(eZTemplateCacheBlock::keyString($keys), $nodeID);
     return eZTemplateCacheBlock::handle($cachePath, $nodeID, $ttl, $useGlobalExpiry);
 }