|showing how the concertina folds into the spine|
...and the other thing that shouldn't be overlooked is the perforations. As you can see from this picture, perforations can look great, even beautiful. These perfs. only look this good because the designer took the time to explain what he wanted to the printer. There are a selection of different perforation "bars" available at print finishers - so do ask a printer to get samples and to show you different types. If you don't convey your expectations to the printer, then they'll generally use the perforating bar that's on the machine and you may be disappointed.