see also Paratexts
(from source ) - "EXTRA-TEXTUAL MEANING: Meaning that originates not in the text being read, but in another related text. The most common type of extra-textual meaning is an allusion, in which an author briefly refers to a character, event, place, or object from the Bible, mythology, history, or another literary work. Since the author does not necessarily explain this allusion, it is up to the reader to recognize the reference and supply the significance from the outside text."
from source - (Johnathan Gray's reponse) "And though I like "extratextuals" (the title of my blog!), "extra" means "outside of," whereas "para" suggests a more complicated relationship to the film or show, outside of, alongside, and intrinsically part of all at the same time. "