The orders a list of playlists comes in, the first being the default one: updated, by playlistActivity, the latest first; new, by creation, the newest first; dumps, the fullest first. GET /api/playlists and GET /api/users/:key/playlists take one as ?sort=, the /playlists page and a profile's playlists tab show them as tabs and keep the one picked in their URL's ?sort=.