This is intended as a hidden doorway, but it's a reasonable way to design closet doors. That's because you're not expecting furniture to be placed in front a closet door. So, adding shelving makes use of that otherwise dead space.
Hidden Doors What could be cooler than having a door that’s completely concealed when it’s closed? One so secret that until you open it, no one else even knows it exists. Hidden doors are typically attached to large bookshelves but can be found behind other seemingly ordinary things, too, like life size pieces of art.