https://github.com/ampproject/amphtml/blob/master/caches.json https://github.com/ampproject/amphtml/blob/master/caches.jso... Google, Bing, Cloudflare are the

https://github.com/ampproject/amphtml/blob/master/caches.json https://github.com/ampproject/amphtml/blob/master/caches.jso... Google, Bing, Cloudflare are the three official caches, which is what I think they mean.