This is an improved Script property, abbreviated "scx"; details in the documentation changes. I didn't add this to 5.14 because I misread the documentation as saying it was provisional. What it actually says is that the data within it is provisional, and subject to change, as they go through the Unicode db and sort things out. It would be nice to have something like "use re 'scx'" that would say, "I want this substituted for the old sc property everywhere in this scope." But the easiest way of doing this would require changes that need to be deferred until the impending battle about 5.16 is settled.