public function register_extensions() {
		$extensions = func_get_args();

		foreach ( $extensions as $extension ) {
			if ( $extension instanceof Twig_ExtensionInterface ) {
				$this->add_extension( $extension );
			} else if ( is_string( $extension ) && class_exists( $extension ) ) {
				$this->add_extension( new $extension );
			} else {
				foreach ( (array) $extension as $ext ) {
					$this->register_extensions( $ext );
				}
			}
		}
	}