You can't get it from the DTCC site now, because they made it disappear. But HERE is the original pdf as saved to archive.org.
This is the "Tag every share and make sure the same share can't get loaned out twice" rule, and a bunch of people think that it means game over for naked shorting.
Which given the fuckery of how this thing looks like it's being handled, may be exactly right.
I'm not sure if it sparks the squeeze or not, but I don't see how they can even implement it in the current system. What are they going to "tag" as "lent out" anyhow? There are millions of counterfeit shares. This probably is the thing that either triggers the MOASS or shines a bright light on the fuckery, and as such, we should all be contacting our representatives and the SEC and whoever will listen and take up the cause.