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I have a public PHP project in a GitHub repo, which contains just one branch (master).

I want to have a separate branch/fork that is private for me (I have paid for private GitHub repos). I would like to be able to merge changes from the private branch/fork to the public repo, and vice versa.

With that in mind, here are my questions:

1. Can I have a private branch on a public repo?
2. Can I fork my own public repo into my own private branch/fork?
3. If both of the above are possible, which is the best way forward? If neither, how should I proceed?

Answers

1. Duplicate your repo.
2. Make the duplicated repo a private one on GitHub.
3. Clone the private repo to your machine
4. Add a remote to your public repo (git remote add public git@github.com:...)
5. Push branches with commits intended for your public repo to that new public remote. (make sure you don't accidentally commit private-only code)
6. You can bring in changes to your public repo using 'git fetch public' and then merge them locally and push to your private repo (origin remote).