Genre. Content

Are the characters wearing this kind of hat? Then it's probably a Western.

E.g. Westerns always have cowboys, whether they are set in the present day or the 1840s. Audiences have a set of expectations as to what a genre text will contain in terms of transportation, costume, character, setting, mise en scene, soundtrack, stars etc, and they look forward to seeing genre-specific examples of content when they experience the text.