Differences to React: supported React child types

[quizzl]

I recently ran into a mismatch in supported child types migrating a codebase with Immutable.js lists:

import { List } from 'immutable'
class App extends Component {
  render() { return <div>{List([42])}</div>; }
  // React renders 42, default preact silently fails
}

This difference is obvious with preact/debug and we get "Objects are not valid as a child.", but it's a confusing surprise if you're used to it and lists stop showing up, especially if they're not used everywhere.

I'm not sure how many child types differ in support between Preact and React. If it's so many that it's not worth maintaining a list, then I think some advice about enabling preact/debug during a migration and looking for failing child types is helpful, and I'd gladly write a PR for it.