In 2017 the Kodokan recognised 3 new osaekomi-waza classifications:
|ura-gatame||historically has referred to multiple pins, but in modern use refers to a hold with one's back to uke and control of the near arm and leg.|
|ushiro-kesa-gatame||long established variant of kesa-gatame, demonstrated in numerous Kodokan materials.|
However I have not encountered any official materials actually defining uki-gatame. Mikinosuke Kawaishi historically used the term to refer to the "knee on belly" position,1 but numerous modern judo videos 2 3 demonstrate the "S-mount" instead.
How do the Kodokan (and/or IJF) define uki-gatame?