Are Paper Mario 1&2 Books or Plays?

[Evil Yoshi Toes]

Something weird goes on with the Paper Mario series. The first game opens up as a play, but battle arenas appear more like dioramas or pop up books than stages though they do have some staged quality to them. Paper Mario 2 opens up as a book but battle arenas are very obviously stages.

It seems very odd to me that the sequel would change the opening from a play to a book while also changing the in game battle arenas to look less like books and more like plays.