Thomas wrote:
You can at least Find and Select by Elevation.
Which means that if you first Select All in your 3D window like you described, then you can filter that (+) or (-) according to Elevation, and that should make possible what you want.

In a perfect world yes.
In this case, I have to change a storey level that was wrongly evaluated and consecutively move down the objects of this storey. In fact, my demand is the outcome of a mess about levels. And into a large survey. So, a search by storey would clean up the mess quite easily. But of course, I am the only one dealing with some junk, right?
Thanks anyway, I'll add a wish, maybe...

Erika wrote:
You could start by going to that story in the floor plan window and using the single story marquee.

same as filter the 3d. A lot of "+1 storey" are shown because they are turned to "all relevant stories". Even worst AFAIR, the marquee capture -1 stairs.