private function addManagedExtensions(RendererAdapterInterface $rendererAdapter)
    {
        $key = $this->getRendererAdapterKey($rendererAdapter);
        foreach ($rendererAdapter->getManagedFileExtensions() as $ext) {
            $rendererAdapters = array($key);
            if ($this->manageableExt->has($ext)) {
                $rendererAdapters = $this->manageableExt->get($ext);
                $rendererAdapters[] = $key;
            }

            $this->manageableExt->set($ext, $rendererAdapters);
        }
    }