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.
'x-foo-component',
          {'blah" onclick="beevil" noise="hi': 'selected'},
          null,
        );
        ReactDOM.render(element, container);
      }
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toEqual(
        'Warning: Invalid attribute name: `blah" onclick="beevil" noise="hi`',
      );
    });
    it('should reject attribute key injection attack on update', () => {
      spyOn(console, 'error');
      for (var i = 0; i < 3; i++) {
        var container = document.createElement('div');
        var beforeUpdate = React.createElement('x-foo-component', {}, null);
        ReactDOM.render(beforeUpdate, container);
        var afterUpdate = React.createElement(
          'x-foo-component',
          {'blah" onclick="beevil" noise="hi': 'selected'},
          null,
        );
        ReactDOM.render(afterUpdate, container);
      }
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toEqual(
        'Warning: Invalid attribute name: `blah" onclick="beevil" noise="hi`',
      );
    });
    it('should update arbitrary attributes for tags containing dashes', () => {