You're absolutely correct in stating REST is not confined to HTML, CSS, JS. A JSON, XML, or binary-based media type are all compatible with the architectural st

You're absolutely correct in stating REST is not confined to HTML, CSS, JS. A JSON, XML, or binary-based media type are all compatible with the architectural style. I don't think the grandparent implies otherwise, though. They are using the browser/HTML example to describe the particular mechanics of client/server interaction, which are key to a REST application. They also bring up "decoupling the client and server (in terms of prior knowledge)". As far as I understand, this isn't about an ability of an arbitrary client to talk to the server. This is, again, easier to explain using the web browser as an example, but the principle equally applies to any client. Think of a "traditional" web application (Django, RoR, etc). Say, one day you decide to completely rewrite it -- add new pages, remove some existing pages, change the site structure (as in which pages the user can navigate to from a given page). While the app has changed beyond recognition, the user doesn't need to download a new version of browser, they can still point their existing browser to the app's home page and it will just work. Now, all of the above should hold for a RESTful app based on a binary media type. I believe, this is the key point of going REST-way. There's a trade-off, of course. While the client is decoupled from the server along one axis, they are fundamentally coupled along another. Imagine a RESTful banking app, and let's say we would like to add a list of recent transactions to the home screen of a mobile client, but the server resource representing the home screen doesn't encode this list in any way. Well, there's is no way to just add it on the client in this case, at least without breaking the principles of REST hence defying the whole purpose of choosing this architectural style in the first place. We have to change the backend code in this case. I can readily see how the limitation described above might be a deal-breaker for a lot of apps as we know them today.