As far as I can tell the OSM wiki page on junction=roundabout ( https://wiki.openstreetmap.org/wiki/Tag:junction%3Droundabout ) does not mention channelized roundabouts, a.k.a turbo roundabouts ( https://en.wikipedia.org/wiki/Roundabout#Turbo_roundabouts ), which are growing like mushrooms in some parts of Europe.
Lanes in such a roundabout are spiraling out. It is normally required for a driver to chose the correct entering lane based on the desired exit. Usually it is not possible to make a full circle, i.e. to exit on the same road as entered - but there may be exception for some of the approaching roads.
It would be nice to add a section to the above page, explicitly stating the preferred way of mapping such roundabouts. Are these roundabouts at all?