The term could easily be used to describe an onboard loo.

Here are photos from my S560, which was ordered with the CB.
At the rear, there is a round sort of plug, which just slips into a hole in the steel frame behind the seats. At the front, there is simply another sort of protrusion, with a knob to turn it. Insert into the hole in the top trunk metal frame and twist the knob to secure. Goes in and out in less than 20 seconds. Good luck.

Many many thanks. I saw today my non-comfort box ordered S550 indeed has those holes, i have the comfort box at the office, will set up next week (I need the trunk space for luggage without the box). THANK YOU! amazing how imcoukdn’t find trunk (okay, boot) photos anywhere on the net.

next question, can you install the trunk hooks even if you have the boot box/comfort box? I doubt you could pull them down with the rails in place, but maybe have them, and then for,non-comfort box days have those package hooks available...
thanks for any thoughts.

follow up - nothing like quoting myself (or laughing at my own jokes). I bought the 2015 comfort box used on eBay, about $160or so shipped. Today finally tried it -success! (After seeing the model number was NOT c9moatible based on a Mercedes site,
possibly in England). Went right in, no issues. I noted 2 things:
1) fully extended, or I think at it’s limit, it’s able to sit on the trunk floor, so that was a nice surprise to me. I think that would let it hold more than it’s rated 20 pounds (limited by floor strength, and lateral forces on the sides versus up and down pressure), and
2) my car clearly did not have the comfort box option from the factory.

hope this helps anyone interested!