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.

return props.children;
      }
      function Owner() {
        
        
        
        return (
          <Parent>
            <input dangerouslySetInnerHTML={{__html: 'content'}} />
          </Parent>
        );
      }
      expect(function() {
        ReactDOM.render(<Owner />, container);
      }).toThrowError('\n\nThis DOM node was rendered by `Owner`.');
    });
    it('should emit a warning once for a named custom component using shady DOM', () => {
      if (ReactDOMFeatureFlags.useCreateElement) {
        spyOn(console, 'error');
        var defaultCreateElement = document.createElement.bind(document);
        try {
          document.createElement = element => {
            var container = defaultCreateElement(element);
            container.shadyRoot = {};
            return container;
          };
          class ShadyComponent extends React.Component {