Power Steering reservoir vent & overflow??

In preparation for flushing and refilling the power steering system on my 360 Modena, year model 2000, European version, I did some reading.

I learned that a metal cap for the power steering reservoir came with the CS version but my ordinary Modena should have a black plastic cap, which it does. However, my car has a vent and an overflow tube attached to the cap. The digital workshop manual shows the metal cap and no sign of an overflow tube.

This 10mm OD rubber hose is connected to a short piece of smaller diameter hard tube which is simply plugged into a hole in the edge of the cap where the fluted edge is. You have to unplug the tube in order to turn the cap and that seems a bit odd to me from an engineering standpoint. It's just a friction fit and it seems to stay put, but it just seems not quite normal.

I'm wondering if someone added this overflow tube? The job is nicely done, but it doesn't strike me as a factory feature.

Should the cap be vented and should it also have an overflow tube?