replication scopes in WAL

[Sergey Shelukhin]

Hi. I am looking at converting WAL to PB and I see replication scopes in
WAL record.
Is there any documentation on those? The usage from code is not obvious,
there seems to be some usage implied that is not there.
If they indicate which KVs to replicate, wouldn't it be better to store
bitmask or something like that?