Are you familiar with the documentation format for our API sites? Assuming we set up api.globalizejs.com, we'd port these docs to that format. That doesn't really answer your question, but it might help to consider the format to figure out what to document how and where.

In general I'd avoid documenting both variants everywhere. We should have docs for the two patterns in one place, along with "You can use instance methods to replace the `locale` argument" and an example or two.