[billyhoffman]

Agreed, and thanks for bring up the Accept header. The author seems uninformed about HTTP's built in Content Negotiation. They write about servers using the User-Agent header, specifically talking about WebP. Accept: "image/webp" works just fine for the major CDNs regardless of the UA.

[admax88q]

Accept and content negotiation has a long established history, and content negotiation is different than the server making decisions based upon metadata.

It's one thing for the client to say "give me this resource in this format" its another for the server to say "oh you're coming from version X.Y of OS Z, I know what you really want."