/**
* Registers an extension.
*
* @param ExtensionInterface $extension An extension instance
*
* @api
*/
public function registerExtension(ExtensionInterface $extension)
{
$this->extensions[$extension->getAlias()] = $extension;
if (false !== $extension->getNamespace()) {
$this->extensionsByNs[$extension->getNamespace()] = $extension;
}
}