*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.
render() {
          return <div>Child2</div>;
        }
      }
      class Child3 extends React.Component {
        render() {
          return <div onclick="1">Child3</div>;
        }
      }
      class Child4 extends React.Component {
        render() {
          return <div>Child4</div>;
        }
      }
      ReactTestUtils.renderIntoDocument(<Parent />, container);
      expectDev(console.error.calls.count()).toBe(2);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('className');
      var matches = console.error.calls.argsFor(0)[0].match(/.*\(.*:(\d+)\).*/);
      var previousLine = (matches || [])[1];
      expectDev(console.error.calls.argsFor(1)[0]).toContain('onClick');
      matches = console.error.calls.argsFor(1)[0].match(/.*\(.*:(\d+)\).*/);
      var currentLine = (matches || [])[1];
      
      
      expect(parseInt(previousLine, 10) + 12).toBe(parseInt(currentLine, 10));
    });
    it('gives source code refs for unknown prop warning for exact elements in composition (ssr)', () => {
      spyOn(console, 'error');
      var container = document.createElement('div');
      class Parent extends React.Component {