[jeffparsons]

I've used the Google docs as a reference to build software that parses '.proto' files and then generate code based on what I found. The docs are... incomplete, ambiguous, and in some places directly contradict the behaviour of protoc. So they're okay as a guide for learning how to write '.proto' files by hand, but a specification they are not.

It's been several years, so I can't point you to specifics. But if you look at open source projects that parse '.proto' files and do anything interesting with the result, you'll probably find lots of comments to the effect of "docs say X, but we are doing Y because that's what protoc does".