The Book of Forbidden Knowledge is an interesting work; as a bric-a-brac, and technically a grimoire, it compiles both skeptical and positive appraisals of different occult and spiritist practice, from the crafting of talismans, to the use of black magic, to protective charms, fortune telling, ceremonial magic, and other topics. It accepts much of its own content at face value, while debunking one infamous instance of the use of the "spirit-closet" and likely had multiple authors.
In its compiled form it is similar to the Petit Albert, the Black Raven, or Hohman's "Pow Wows." It additionally wanders into topics such as omens (good and ill), superstitions in general, and a few elements of folk medicine.