*feature*

>Warning: A component is `contentEditable` and contains `children` managed by React. It is now your responsibility to guarantee that none of those nodes are unexpectedly modified or duplicated. This is probably not intentional.

It would help heaps if I would know _which_ component is causing this.
return <FancyTable><FancyRow /></FancyTable>;
      }
      function App2() {
        return <Viz2 />;
      }
      ReactTestUtils.renderIntoDocument(<App2 />);
      expectDev(console.error.calls.count()).toBe(2);
      expectDev(
        normalizeCodeLocInfo(console.error.calls.argsFor(1)[0]),
      ).toContain(
        '\n    in tr (at **)' +
          '\n    in Row (at **)' +
          '\n    in FancyRow (at **)' +
          '\n    in table (at **)' +
          '\n    in Table (at **)' +
          '\n    in FancyTable (at **)' +
          '\n    in Viz2 (at **)',
      );
      ReactTestUtils.renderIntoDocument(<FancyTable><FancyRow /></FancyTable>);
      expectDev(console.error.calls.count()).toBe(3);
      expectDev(