>But yes the client still has to know what to do in advance.

According to Roy Fielding[1] (who came up with the concepts of ReST and HATEOAS:

"A REST API should be entered with no prior knowledge beyond the initial URI (bookmark) and set of standardized media types that are appropriate for the intended audience"

So if an application doesn't rely on "standardized media types", and "the client still has to know what to do in advance", then it seems like whatever you're doing, it isn't HATEOAS after all.

[1] http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hyperte...