(I took a spill on a stairway last year in a German building owned by my employer. Amazingly, the step edges were not highlighted -- if anything they were occluded by the fancy stone patterns, and my d***ed bifocal glasses prevented me from seeing the step edges clearly.* Fortunately the only thing hurt was my ego, but it could have been worse.)
(* Stairs have been h*ll since I finally wound up wearing glasses.)
Oh.. I see what you mean, actually, I was referring to 'ploughing' the strings, not the steps.
But, speaking of legalities regarding steps - it's a minefield over here, steps under a certain width can lead to lawsuits if an injury occurs - fine, but the problem is planning engineers often don't design the hallways of houses with staircases in mind - it's often a tight squeeze to get the step within regulation - but engineers have their bases covered, so it's the manufacturer who gets the blame if anything goes wrong! :(
As it happens, though - we haven't made any unusual stair threads.