Dataflow is one of the most daunting areas for contributors to the project system. We have various bits of documentation spread across several repositories but most of it is fairly advanced or provided without enough context to know whether it's relevant to what you're trying to do. We should have a single document that walks the reader through all the relevant concepts, building things up in a thought-out fashion, that is both readable top-to-bottom and as a reference for specific topics.
This is now ready for review. There are some small sections at the end that could be populated, but I'm less clear on that content so am happy to merge as-is for now.
From https://github.com/dotnet/project-system/issues/9099:
This document aims to provide that.
I'm putting this draft PR up to gather feedback.