Official...whatever that means in this case.
There are a bunch of options in the list already, so I assume there must be some importance to picking the correct one.
I don't know how the whole shabang works, but I'm thinking that if I leave it as 1252 Latin 1 and I have the fraction 1/2 in the bracketleft position, maybe it could, for example, goof something up in some systems and print a % instead.