(2) Many kinds of fiction are self-explanatory: mysteries, westerns, love stories, spy thrillers, and science fiction define themselves by the terms used to name them. The horror story is less easily defined, perhaps because other types of fiction so often use the trappings of terror to enhance their plots. Charles Dickens used the vehicle of an old-fashioned ghost Story to tell “A Christmas Carol”, but that book is not a horror story. Nor does a Grimm brothers fairy tale such as “Hänsel and Gretel,” with its child-devouring witch, belong to the genre.
 In this paragraph, the sentence “Many kinds of fiction are self-explanatory” means（）.