Serial number zero and sequence space arithmetic

[Cricket Liu]

Hi, folks.

I have a question about when BIND began using sequence space
arithmetic and when it stopped using the serial number 0 to mean
"always transfer this zone."

It looks to me from the 4.9.3 source like sequence space
arithmetic came in at about 4.9.  (I don't have any 4.9 source
older than 4.9.3, and 4.8.3 doesn't appear to use sequence
space.)  Can anyone confirm this?

Serial number 0 is special cased as far back as 4.8.3.  I've
got several versions of BIND 8 that show signs of it, too.
Can anyone tell me if and when the serial 0 logic was
removed?

Thanks!

cricket