In git, we solve this problem by sticking a .gitignore file in any directories we want to be part of the repo, but without the contents (cache folders, user-generated data destinations, etc.)
I think the author was referencing hg's numerous extensions. In reality I think both git and hg users turn to Google when they get stuck (same for bzr, svn, cvs, and every other scm).
I always start googling and hoping there's a stackoverflow question about it that has an answer that I don't get.