The man page you linked covers this.- depending on whether nl or nonl was called, pressing "Enter" on the regular keyboard may return either a carriage-return or line-feed, and finally
Sounds like one of those things that's hard to nail down.
Different keyboards, OS's, and any number of different
implementations going back to the 60s. Even that man page -- I
have no idea how well it meshes with zcurses, only that it seemed
close. '\n' will do fine.