The documentation page on exposition formats states:

A server will prefer receiving the protocol-buffer format, and will fall back to the text-based format if the client does not support the former.

As of Prometheus 2.0.0, this is not true. It doesn't seem to support the protobuf format at all.

That section of prose should be updated to reflect that fact, and the Supported in secton of the comparison table should reflect the upper version bound, at a minimum. More generally this page could probably stand to be rewritten to reflect conclusions from, for instance, this discussion.