Self-reference
A reference that names an imaginary source is in some sense also a self-reference. A self-reference automatically makes a comment about itself. Premises that name themselves as premises are premises by self-reference; conclusions that name themselves as conclusions are conclusions by self-reference.
In their respective imaginary worlds the Necronomicon, The Hitchhiker's Guide to the Galaxy, and the Red Book of Westmarch are realities, but only because they are referred to as real. Authors use this technique to invite readers to pretend or to make-believe that their imaginary world is real. In the sense that the stories that quote these books are true, the quoted books exist; in the sense that the stories are fiction, the quoted books do not exist.
Read more about this topic: Object Of The Mind