Which shuffle does the 'Always shuffle this playlist' option pick up?

Currently, it always does an unbiased random shuffle. It should probably do something cleverer, but it'd have to be much cleverer, as this option only shuffles the children of the playlist where it's set, not any more distant descendants. Of course typically the children of the root playlist are other playlists, and don't have tags for play_count, last_played, year, duration, etc.

Peter