Todo

• Document intuitions behind the extension testing logic
• Try to automate using TS as ground truth for tests

Document intuitions behind the extension testing logic

I imagine people are curious to understand the rules for deciding whether one type extends another, if only to judge if they can rely on the logic present in this package.

It should also make it easier for others to reproduce the logic in other frameworks.

Try to automate using TS as ground truth for tests

It seems ideal to take TypeScript as a ground truth, and, given the TS compiler, possible to automate evaluating tests against it.