This usually means that the user mixed up our lowercase/uppercase naming convention; see https://github.com/facebook/react/pull/3429#issuecomment-85166440.

We could add a message like

> Warning: The tag <commentBox> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

We'd check this only once per tag and only in development mode.

var addendum2 = ReactDOMFeatureFlags.useFiber
        ? '\n    in tr (at **)' +
            '\n    in Row (at **)' +
            '\n    in table (at **)' +
            '\n    in Foo (at **)'
        : ' See Row > tr > #text.';
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(1)[0])).toBe(
        'Warning: validateDOMNesting(...): Text nodes cannot appear as a ' +
          'child of <tr>.' +
          addendum2,
      );
      var addendum3 = ReactDOMFeatureFlags.useFiber
        ? '\n    in table (at **)' + '\n    in Foo (at **)'
        : ' See Foo > table > #text.';
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(2)[0])).toBe(
        'Warning: validateDOMNesting(...): Whitespace text nodes cannot ' +
          "appear as a child of <table>. Make sure you don't have any extra " +
          'whitespace between tags on each line of your source code.' +
          addendum3,
      );
    });
    it('gives useful context in warnings', () => {
      spyOn(console, 'error');
      function Row() {
        return <tr />;
      }
      function FancyRow() {
        return <Row />;
      }
      class Table extends React.Component {