It seems problematic to allow arbitary non-lowercase attribute on HTML nodes. Because the server has no ability to keep them case sensitive (HTML isn't). So they will end up different on the client.

We should probably warn if the attribute is not a known one *and* is not lowercase.
itRenders('a select value overriding defaultValue', async render => {
        const e = await render(
          <select value="bar" defaultValue="baz" readOnly={true}>
            {options}
          </select>,
          1,
        );
        expectSelectValue(e, 'bar');
      });
      itRenders(
        'a select value overriding defaultValue no matter the prop order',
        async render => {
          const e = await render(
            <select defaultValue="baz" value="bar" readOnly={true}>
              {options}
            </select>,
            1,
          );
          expectSelectValue(e, 'bar');
        },
      );
    });
    describe('user interaction', function() {
      let ControlledInput,
        ControlledTextArea,
        ControlledCheckbox,
        ControlledSelect;
      beforeEach(() => {
        ControlledInput = class extends React.Component {
          constructor() {