> I think a kinder reading of this point is “a 2xx response means you can parse the thing you were expecting to parse”
It doesn’t though.
Even with an Accept header on the request, it is not impermissible for a server to return a 2xx result with a different format indicated by the Content-Type header if it cannot, for whatever reason, return a result in a requested format (it may also, consistent with the HTTP spec, return a 406 Not Acceptable or, if it wants to be cagey about a resource representation existing if there is none matching the Accept header, 404 instead.)
If you want to know whether and how you can safely parse the response, the HTTP compliant way is to read the Content-Type header. Otherwise, you are relying on assumptions (which may be valid for out-of-band, non-HTTP reasons) about behavior that are outside of the spec.
It doesn’t though.
Even with an Accept header on the request, it is not impermissible for a server to return a 2xx result with a different format indicated by the Content-Type header if it cannot, for whatever reason, return a result in a requested format (it may also, consistent with the HTTP spec, return a 406 Not Acceptable or, if it wants to be cagey about a resource representation existing if there is none matching the Accept header, 404 instead.)
If you want to know whether and how you can safely parse the response, the HTTP compliant way is to read the Content-Type header. Otherwise, you are relying on assumptions (which may be valid for out-of-band, non-HTTP reasons) about behavior that are outside of the spec.