Authors may say whether they describe or prescribe. For two reasons the problem is particularly fascinating for students of Popper's views. This makes Professor Jarvie's study exciting. Popper's theory is then both prescriptive and descriptive of the better practices. Also, the logic that Popper said suffices for science is the logic of the situation, not logic in the narrow sense of the word.
Any activity obeys some rules, and they are known as the logic of that activity.
Similarly one speaks of the rules of the game, where the game is the institutionalized activity in question. Methodology is such a game. This general question has no general answer, though for special cases special answers are available. In the arts the rules are more liberal, especially in the West. But everywhere rules limit variation, and at times they are broken.