This is Diana Wynne Jones' hilarious skewering of the many tropes and clichés of fantasy fiction. It is structured as a guidebook written for a traveler, to help them make sense of or prepare for their journey through Fantasyland. The book, after an initial intro, is ordered into alphabetical sections, each of which starts with a "gnomic utterance" and has entries for places, features, or stock characters in the many worlds of Fantasyland. Throughout, the entries refer to things that "the Management" may or may not do (the managers organizing your tour through Fantasyland, of course-- i.e., the authors), and many of the entries have italicized phrases of words marked with "OMT" to indicate an "Official Management Term" (for those phrases or adjectives that somehow seem to always get used in Fantasy novels).
