Supporting the folding platform was tricky, because it needs to be free of obstructions above, below and on three sides. The only place it can be supported is from above at the input end, and you can see it pivoting on the shaft with the spring clips. You can also see one of the rubber bands that supplies tension to press the platform down onto the centre roller. The design is a compromise between applying enough pressure for the paper not to slip, and not applying so much pressure that the platform bends, because it must be kept thin to achieve a good fold.
The small rectangular gap in the platform is the hole for an optical sensor which detects when the paper has reached the correct position for folding.
Click on the pictures at right for some more views of the folding mechanism.