Disagree. From my experience as a scientist there isn't a manual that says what peer review is and isn't supposed to be. Of course, some journals have such guid

Disagree. From my experience as a scientist there isn't a manual that says what peer review is and isn't supposed to be. Of course, some journals have such guidelines (not that all reviewers read them), and the editors who assign the reviews are free to ignore a rogue reviewer. But there is a set of explicit or tacit standards of good science, and any of it is fair game in peer review: 1. Validity of the experiment 2. Interestingness / novelty of the work 3. Appropriate choice of methods and correctness / believability of the results 4. Signs of outright fraud (suspicious figures, etc.) Absolutely if I notice some weird Photoshop artifacts in a figure, or some other obvious sign of fake data, I'm going to call that out. I'm probably an outlier on this next one, but I've even been tempted to reject articles just for having egregiously, unreadably bad writing. I know this will be regarded as bias against people whose first language is not English, but if the writing is so bad that it stands in the way of making sense of the article, and the authors can't be bothered to get a decent editor, it's not a worthy contribution to the (English language) scientific literature.