Unlike a Potter film or computer game, the authors of the Lexicon encyclopedia are not simply moving Potter to another medium. Their purpose, rather, is providing a reference guide with description and discussion, rather like a very long and detailed book review. Such guides have been around forever—centuries if you count the Bible, and more recently for complex works like the writings of Jorge Borges or The Lord of the Rings. As long as a guide does not copy the original work verbatim, it falls outside the category of “adaptation.” And that’s why it is largely unnecessary to discuss the more complex copyright doctrine of “fair use.” Rowling’s rights over the guide don’t exist to begin with, so we don’t need to go there.

I shouldn’t have to say this, but here goes: suing people is like going to war. If you’re going to go to war with tens of thousands of your customers every year, don’t be surprised if they start treating you like the enemy.