So. Heres the backstory for the setting: A Wizard Did It.
Heres the long version:
One day, a nameless wizard realized he didn't have much time left, and he still didn't have a magnum opus. So he used what he had. His library, his magic, and a walnut. He crammed all his magic, and all his media into the walnut. Then he shot it into space.
It found a nice demiplane and took root. From there, the very very long spell began. First it formed a library. That library defined the world around it, and was in turn defined by the world around it. Then it grew a grand tree. From there a few civilizations were seeded by the medias shoved into the walnut.
This library's most important book is its World Book. A book that is the story of itself. The library has reference biographies of every living being in the demiplane.