Interested in adding toolchain support for MSVC

I don't see any toolchain support for MSVC. The documentation is light in this area, so it's not even clear what the low level anatomy of a toolchain file even is. I've looked at the zig toolchain for inspiration, but there's a lot of magic syntax in the files that isn't really explained anywhere.

I think it would help to have a guide "How to add support for a new toolchain" that describes in detail what all the various commands do, overall syntax rules for the file (it looks like python, but not quite), and anything else that someone with no experience with bazel or buck might need in order to get started.

In the meantime, what's the best place to start poking if I want to try to get MSVC support working?