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.

props = ReactDOMOption.getHostProps(this, props);
        break;
      case 'select':
        ReactDOMSelect.mountWrapper(this, props, hostParent);
        props = ReactDOMSelect.getHostProps(this, props);
        transaction.getReactMountReady().enqueue(trapBubbledEventsLocal, this);
        
        
        ensureListeningTo(this, 'onChange', transaction);
        break;
      case 'textarea':
        ReactDOMTextarea.mountWrapper(this, props, hostParent);
        props = ReactDOMTextarea.getHostProps(this, props);
        transaction.getReactMountReady().enqueue(trackInputValue, this);
        transaction.getReactMountReady().enqueue(trapBubbledEventsLocal, this);
        
        
        ensureListeningTo(this, 'onChange', transaction);
        break;
    }
    assertValidProps(this, props);
    
    
    var namespaceURI;
    var parentTag;
    if (hostParent != null) {
      namespaceURI = hostParent._namespaceURI;
      parentTag = hostParent._tag;
    } else if (hostContainerInfo._tag) {
      namespaceURI = hostContainerInfo._namespaceURI;