The FLAT CAP REAR attaches to the Rear Surface of all Center Sections as well as directly to a Front End Cap.
The FLAT CAP REAR module offers one flat pocket on the outside, and one flat half-height slip pocket on the inner surface of the module. The primary outer pocket is accessed from the top and has a cover flap that is secured with Velcro. This where you'll likely store your iPad (as long as it's not in a thick case), or a manila folder or two for some documents, or a magazine.
There is a pair of one-third-height panels on the outer-most surface of the module. The upper panel has the unique ability to tuck and untuck the lower panel. When untucked, the opening allows the telescoping tubes of a suitcase or folding cart to pass through and the panel serves to secure your bag to those tubes (especially when this FLAT CAP REAR is attached to other modules to form bigger bags like the B2 COMPUTE, B4 SWIFT or the B7 FLIGHT.) When the upper panel is tucked back into the lower panel, the combination of both panels work together to serve as a thin two-thirds-height slip pocket.
There is also a flat half-height slip pocket on the inner surface of the module. It has a cover flap secured with a spot of Velcro. Here you can stow an important document or two, or any small flat item that you'd like to keep out of harm's way.
The FLAT CAP REAR is one-directional (as are ALL of the FLEX System modules). It is always Rear-facing. That means that it can only be zipped onto the rear surface of any module. You cannot zip a FLAT CAP REAR onto the front of any other FLEX module.
The good news is that there is an identical-looking, yet opposite version, which is called the FLAT CAP FRONT. This opposite module is always front-facing, so it will zip on the the front surface of any module. The idea is that if someone wanted to, they could put a FLAT CAP onto both the front AND the rear of a configuration, thus giving a nice slim look to the bag.