Tony Vargas
Legend
So, not a module.The latter, though it can be a replacement or supplement.
Sorry, I get persnickety about the meaning of 'modular.' There was noise during the playtest that 5e might be modular, there was never any development to indicate it was going in that direction, and it ultimately wasn't modular. It was DM-Empowering,. put some rules in the option ghetto/enshrined others as somehow non-optional, and it is clearly very open to variants, including presenting some official variants. Which does not add up to the same thing as 'modular.'