public function getOriginalNodeNames()
    {
        if (null === $this->originalNodeNames) {
            if (self::INITIALIZED_FROM_COLLECTION === $this->initialized) {
                $this->originalNodeNames = $this->collection->getKeys();
            } else {
                $this->originalNodeNames = (array) $this->getNode($this->fetchDepth)->getNodeNames($this->filter);
            }
        }

        return $this->originalNodeNames;
    }