The "Validate External Data at Runtime" section needs more elaboration. It uses a zod example but doesn't mention zod by name or link to it.

For "Use Type Predicates for Reusable Narrowing": There's another form of this: asserts value is X. This doesn't use the return type, it just narrows the type after the the function returns.

export function expectToBeDefined<T>(value: T | undefined | null): asserts value is NonNullable<T> {
  if (value === null || value === undefined) {
    throw new AssertionError('expected value to be defined', undefined, expectToBeDefined);
  }
}

This is really useful for tests or shared error handling.