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.

parentTag = hostContainerInfo._tag;
    }
    if (
      namespaceURI == null ||
      (namespaceURI === DOMNamespaces.svg && parentTag === 'foreignobject')
    ) {
      namespaceURI = DOMNamespaces.html;
    }
    if (namespaceURI === DOMNamespaces.html) {
      if (__DEV__) {
        warning(
          isCustomComponent(this._tag, props) ||
            this._tag === this._currentElement.type,
          '<%s /> is using uppercase HTML. Always use lowercase HTML tags ' +
            'in React.',
          this._currentElement.type,
        );
      }
      if (this._tag === 'svg') {
        namespaceURI = DOMNamespaces.svg;
      } else if (this._tag === 'math') {
        namespaceURI = DOMNamespaces.mathml;
      }
    }
    this._namespaceURI = namespaceURI;
    if (__DEV__) {
      var parentInfo;
      if (hostParent != null) {
        parentInfo = hostParent._ancestorInfo;
      } else if (hostContainerInfo._tag) {