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What does lowercase r-s notation mean?

I came across a naming convention which I haven't seen before. I let ChemDraw name the following compound for me and got a name containing lowercase "r" and "s" configurations.

Can someone tell me what this means and something about the actual convention behind it? I think it must have something to do with rings and maybe with some kind of "pseudo-chirality" due to a certain conformation of the ethyl group which is attached to the ring, but I'm only guessing.