We're switching Atom to React, but we want to support backward-compatible shims to our previous view framework.

In the old framework, views were represented as jQuery-wrapped DOM elements. Ideally, we'd like to provide backward-compatible shims by simply rendering the React component and wrapping its root element in a jQuery wrapper with an API that's compatible to our old editor views. That would essentially look like this:

``` javascript
var editorRoot = document.createElement('div')
React.renderComponentWithRootElement(Editor(props), editorRoot)

// the element would actually be wrapped in a custom subclass of jQuery,
// but this is clearer for this example
var editorShim = $(editorRoot) 
```

Currently, this isn't possible because React components need to be rendered into a container. So instead we need to create a wrapper element and render the component inside it. This is sad because it adds an extra layer of markup which confuses styling, and also means that the editor has a wrapper when used via the shim layer but no wrapper when embedded as a child via React itself.

Is there something fundamental preventing React from adopting DOM nodes directly without the parent? Is this something we could even hack in in a way that would be somewhat maintainable?

:heart:

log.push('componentDidUpdate');
        expect(this.divRef.current.textContent).toBe(
          `value:${this.props.value}`,
        );
        expect(snapshot).toBe('foobar');
      }
      render() {
        log.push('render');
        return <div ref={this.divRef}>{`value:${this.props.value}`}</div>;
      }
    }
    const div = document.createElement('div');
    ReactDOM.render(<MyComponent value="foo" />, div);
    expect(log).toEqual(['render']);
    log.length = 0;
    ReactDOM.render(<MyComponent value="bar" />, div);
    expect(log).toEqual([
      'render',
      'getSnapshotBeforeUpdate',
      'componentDidUpdate',
    ]);
    log.length = 0;
  });
  it('should warn if getSnapshotBeforeUpdate returns undefined', () => {
    class MyComponent extends React.Component {