In short, by deciding to sell his material, Vander Ark was stepping across a line. He was no longer just an enthusiastic fan, but a professional and potential competitor — fair game for the lawyers.
The question now for the courts is whether the lexicon itself violates copyright law, and the decision may not be easy.
U.S. rules allow for the "fair use" of copyrighted material in unauthorized works, but there are limits. Journalists may quote from films and books when writing a review. Scholars can use excerpts from a novel while penning an author's biography.