*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.
'If you accidentally passed it from a parent component, remove ' +
          'it from the DOM element.\n' +
          '    in div (at **)',
      );
    });
    it('allows cased custom attributes', function() {
      spyOn(console, 'error');
      var el = ReactTestUtils.renderIntoDocument(<div fooBar="true" />);
      expect(el.getAttribute('foobar')).toBe('true');
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(
        normalizeCodeLocInfo(console.error.calls.argsFor(0)[0]),
      ).toMatch(
        'React does not recognize the `fooBar` prop on a DOM element. ' +
          'If you intentionally want it to appear in the DOM as a custom ' +
          'attribute, spell it as lowercase `foobar` instead. ' +
          'If you accidentally passed it from a parent component, remove ' +
          'it from the DOM element.\n' +
          '    in div (at **)',
      );
    });
    it('warns on NaN attributes', function() {
      spyOn(console, 'error');
      var el = ReactTestUtils.renderIntoDocument(<div whatever={NaN} />);
      expect(el.getAttribute('whatever')).toBe('NaN');
      expectDev(console.error.calls.argsFor(0)[0]).toContain(
        'Warning: Received NaN for numeric attribute `whatever`. If this is ' +
          'expected, cast the value to a string.\n    in div',
      );
    });