public function add_extension( Twig_ExtensionInterface $extension ) {
		$env  = $this->instance();
		$exts = $env->getExtensions();

		if ( isset( $exts[$extension->getName()] ) ) {
			return;
		}

		try {
			$env->addExtension( $extension );
		} catch ( LogicException $e ) {
			return;
		}
	}