Ah! I see, no prob, let me explain.
Ruby on Rails has two sets of official documentation: The Rails Guides
are for learning, and the Rails API is a reference.
They are part of the project, in particular they belong to the project
tree. The API is intermixed with code because it uses RDoc. The guides
have their own stuff below railties/guides. It is a custom set of
.textile source files together with some hand-crafted generators.
Thus, everything lives inside the rails git repository.
When a major release is coming, master is branched. For example, a
while back master was branched to 3-1-stable. In particular the docs
are branched together with everything. So we have now master,
3-1-stable, 3-0-stable, and 2-3-stable. And they have their
The maintenance of the documentation, guides and API, happens in
master. Patches are expected to come with tests and docs coverage. In
particular, if a patch changes something in a guide, it should update
it. A new feature should be explained etc. Thus, the evolution of the
code, its tests, and its docs, go together. (In reality this is not
that perfect, but that's the way it should be.)
Do you see how this works better now?