Git pull request (Github) - where does it merge?

Question

If I fork repo Foobar's master branch and make some edits and then submit a pull request that is approved, my changes get pulled into Foobar's master branch. What if I fork Foobar's master branch but when I make a pull request I want the changes to be pulled into branch xyzzy rather than branch master. How does Github decide which branch to merge the pull request into? Do I need to make a xyzzy branch on my forked repo and then make a pull request from there? Or is there something else I need to do?

Answer 1

When you open a pull request you can choose which you want your changes to be merged into.

Where you see Foobar:master ... YourRepo:master there is a Edit button on the far right which will then allow you to choose a different base branch - see below.