The document discusses how the horror film Insidious establishes its genre through various codes and conventions: 1) It uses low-key lighting, costumes like robes and pale makeup to depict supernatural antagonists and create an ominous tone. 2) The plot involves a family threatened by demons and an evil spirit called "the Further," representing a clear binary opposition of good vs. evil. 3) Elements like scary music, camerawork with close-ups, and a 15 rating further signal to the audience that this is a horror film.