The wiki only provides guidelines on the minimum. There's nothing you can follow for something it doesn't mention. `turning_loop=` is not covered. 
When there are driveways connected to it, it causes ambiguity on whether the untagged section could be a `junction=` `=circular` or `=roundabout` , which is only implicitly indicated by having a `restriction=no_u_turn` at the tail. As the `highway=turning_loop` is improved to a separately drawn road, the same information should be preserved. 
