Run the [`fixtures/ssr` test harness](https://github.com/facebook/react/tree/master/fixtures/ssr). In the terminal, the following warning is logged:

```
Warning: Unknown prop `onClick` on <a> tag. Remove this prop from the element. For details, see https://fb.me/react-unknown-prop
  in a (at Page.js:12)
  in p (at Page.js:18)
  in div (at Page.js:17)
  in Page (at App.js:12)
  in div (at App.js:10)
  in body (at Chrome.js:17)
  in html (at Chrome.js:9)
  in Chrome (at App.js:9)
  in App (at render.js:18)
```

SSR behavior should match client-side behavior and not warn for a valid attribute.
const e = await render(<textarea defaultValue="foo" />);
        expect(e.getAttribute('value')).toBe(null);
        expect(e.getAttribute('defaultValue')).toBe(null);
        expect(e.value).toBe('foo');
      });
      itRenders('a textarea value overriding defaultValue', async render => {
        const e = await render(
          <textarea value="foo" defaultValue="bar" readOnly={true} />,
          1,
        );
        expect(e.getAttribute('value')).toBe(null);
        expect(e.getAttribute('defaultValue')).toBe(null);
        expect(e.value).toBe('foo');
      });
      itRenders(
        'a textarea value overriding defaultValue no matter the prop order',
        async render => {
          const e = await render(
            <textarea defaultValue="bar" value="foo" readOnly={true} />,
            1,
          );
          expect(e.getAttribute('value')).toBe(null);
          expect(e.getAttribute('defaultValue')).toBe(null);
          expect(e.value).toBe('foo');
        },
      );
    });
    describe('selects', function() {
      var options;
      beforeEach(function() {