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.

},
  createElement(
    type: string,
    props: Object,
    rootContainerElement: Element,
    parentNamespace: string,
  ): Element {
    
    
    var ownerDocument = rootContainerElement.ownerDocument;
    var domElement: Element;
    var namespaceURI = parentNamespace;
    if (namespaceURI === HTML_NAMESPACE) {
      namespaceURI = getIntrinsicNamespace(type);
    }
    if (namespaceURI === HTML_NAMESPACE) {
      if (__DEV__) {
        warning(
          type === type.toLowerCase() || isCustomComponent(type, props),
          '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
            'in React.',
          type,
        );
      }
      if (type === 'script') {
        
        
        var div = ownerDocument.createElement('div');
        div.innerHTML = '<script><' + '/script>';