I'm sure it is but most actual fanfic on most websites is not trying to create an ambience of you just stumbled into top secret files and the cops might be at your door any minute for reading them those do not and should not have any kind of warning because the whole point of the website is you shouldn't be reading this most of the articles start with that but in normal fanfiction and I've seen many in the very beginning of the story it lists what kind of sex and what the combinations in the stories are be it human animal or Digimon