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.

switch (type) {
    case 'svg':
      return SVG_NAMESPACE;
    case 'math':
      return MATH_NAMESPACE;
    default:
      return HTML_NAMESPACE;
  }
}
var ReactDOMFiberComponent = {
  getChildNamespace(parentNamespace: string | null, type: string): string {
    if (parentNamespace == null || parentNamespace === HTML_NAMESPACE) {
      
      return getIntrinsicNamespace(type);
    }
    if (parentNamespace === SVG_NAMESPACE && type === 'foreignObject') {
      
      return HTML_NAMESPACE;
    }
    
    return parentNamespace;