Often I got this question from customers.
Look at the following image:
Normally in a plan only objects between the cut plane and the bottom/view depth are visible in plan (some categories will also show when they are between the cut plane and the top).
But in this case the floor is under the bottom/view depth and is still visible in floor plan.
Well, it is so obvious that you want to see the floor in a plan that the developers made an exception for floors. Even when a floor is under the bottom/view depth it is still visible.
You should think that in that case the floor should “touch” the bottom/view depth. range but the exception the developers made is even more flexible: in between the bottom/view depth height and a range of -1219.2mm (4 feet) the floor will be visible in plan.