Document event bubble order

This is documenting the current order in which events are dispatched
when interacting with native document listeners and other React apps.

For more context, check out facebook#12919.

packages/react-dom/src/__tests__/ReactDOMComponent-test.js

@@ -2603,4 +2603,60 @@ describe('ReactDOMComponent', () => {
       expect(node.getAttribute('onx')).toBe('bar');
     });
   });
+
+  it('receives events in specific order', () => {
+    let eventOrder = [];
+    let track = tag => () => eventOrder.push(tag);
+    let outerRef = React.createRef();
+    let innerRef = React.createRef();
+
+    function OuterReactApp() {
+      return (
+        <div
+          ref={outerRef}
+          onClick={track('outer bubble')}
+          onClickCapture={track('outer capture')}
+        />
+      );
+    }
+
+    function InnerReactApp() {
+      return (
+        <div
+          ref={innerRef}
+          onClick={track('inner bubble')}
+          onClickCapture={track('inner capture')}
+        />
+      );
+    }
+
+    const container = document.createElement('div');
+    document.body.appendChild(container);
+
+    try {
+      ReactDOM.render(<OuterReactApp />, container);
+      ReactDOM.render(<InnerReactApp />, outerRef.current);
+
+      document.addEventListener('click', track('document bubble'));
+      document.addEventListener('click', track('document capture'), true);
+
+      innerRef.current.click();
+
+      // The order we receive here is not ideal since it is expected that the
+      // capture listener fire before all bubble listeners. Other React apps
+      // might depend on this.
+      //
+      // @see https://github.com/facebook/react/pull/12919#issuecomment-395224674
+      expect(eventOrder).toEqual([
+        'document capture',
+        'inner capture',
+        'inner bubble',
+        'outer capture',
+        'outer bubble',
+        'document bubble',
+      ]);
+    } finally {
+      document.body.removeChild(container);
+    }
+  });
 });