Hmmm. So, I mostly expect this to be dramas, or at least dramedies, though I suppose it won't necessarily exclude straight-up comedies. Of course films in this category can be set in any place or era, as long as that era is sometime prior to when the film was made... probably more than a few years prior, but it could be as recent as a decade earlier. Though normally I tend to think of this as a category for sort of Victorian British novel adaptations, it can really be anything. What's really important is that the films evoke a sense of the specific era in which they're set, and the feeling that they couldn't happen at all (or at least not in quite the same way) in any other era.
Then again, there may be some movies set in the past which I put in other categories, such as action/adventure, based on a true story, coming of age, family, fantasy, martial arts, musicals, romance, war films, etc., which are themselves definitely specific to the era in which the film is set. So... sometimes my choice of where to put a review will be somewhat arbitrary, and I may not always completely understand that choice, myself....
See also historical fiction, period shows, Masterpiece/Mystery!, and period webseries