GC docs appears segment based not covering regions.

I'm trying to learn more intimately about GC and reading the doco I am confused as it talks only about segments but I thought it is by default moved to regions. I suspect the doco has not been updated but as I am still learning I can't be sure.

See https://github.com/dotnet/runtime/blob/main/docs/design/coreclr/botr/garbage-collection.md