The IJF has just updated its rules. It's not a major update and most rules remain the same. But there are some clarifications about some rules. Unfortunately, the ones relating to Yuko are a bit confusing. Let's have a look at them.
This is considered a yuko. The player is almost completely on her front. 
This is the same landing as seen from another angle. As you can see, the player is almost completely on her front. But this is a yuko.
There are a few more scenarios that warrant a yuko:
Landing on the side with the elbows down is yuko. 
Landing on the side with arms outstretched and palm down, is also a yuko. 
Landing on your buttocks (at least one cheek) with no hands touching the mat is yuko.
Landing on the buttocks (at least one cheek) with elbows out is also yuko.
First major question: Previously, if you land on your buttocks but your upper body is leaning forward, it is NOT yuko. What about now, under the updated rules? Is that situation now a yuko?
There are two more scenarios that merit a yuko:
If you land on the upper back (shoulder blade of either right or left shoulder), it's a yuko. 
If you land on your neck, it's also a yuko.
Now, let's look at NO Yuko situations:
Second major question: What does "landing on the front part of the stomach" really mean? Look at the picture above and the one below. Do these situations look somewhat similar? They are not identical, obviously, but the differences between them are so small, it's really hard for a non-referee to differentiate the two. I suspect some referees themselves would have a hard time differentiating the two scenarios in a live competition setting.
I can't understand why this situation warrants a yuko but the picture above it does not. 
This is easy enough to understand. If uke lands on their knees in a kind of turtle position but one shoulder touches the mat, it's not a yuko.
A natural question to ponder upon: Has this update made judo easier or harder to understand?
