> Depends on what the commenter means by app state. Anything bookmarkable - like search results - should be in the URL, but "state" should not (I consider things like partially filled in forms, shopping carts, etc to be state).

Yes, shopping cart state should be in the URL in the form of a server-side token under which the cart state is stored. Ditto for partially filled in forms, if that's something your app needs.

All page state should be transitively reachable from the URL used to access that page, just like all state in a function in your favourite programming language should be transitively reachable from the parameters passed into that function, eg. no global variables. The arguments for each are basically the same.