public function addEntry(PelEntry $e)
    {
        if ($this->isValidTag($e->getTag())) {
            $e->setIfdType($this->type);
            $this->entries[$e->getTag()] = $e;
        } else {
            throw new PelInvalidDataException("IFD %s cannot hold\n%s", $this->getName(), $e->__toString());
        }
    }