@Theo at a very simple level, comments are for these things:
(a) requesting clarification, in which you actually have to state what's unclear and request clarification. (probably not the case here.)
(b) suggesting an improvement, in which you ought to suggest an actionable improvement. (e.g.: "this should go into more detail on X?", or "Y conflicts with this other rule [link], you need to address this").
(c) the author responding to either of the above.
(d) sometimes, someone pointing out - very solidly, and not as a mere expression of opinion - that someone's comment of (a) or (b) is inval…