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.

transaction,
        props,
      );
      var tagContent = this._createContentMarkup(transaction, props, context);
      if (!tagContent && omittedCloseTags[this._tag]) {
        mountImage = tagOpen + '/>';
      } else {
        mountImage = tagOpen + '>' + tagContent + '</' + type + '>';
      }
    }
    switch (this._tag) {
      case 'input':
        transaction.getReactMountReady().enqueue(inputPostMount, this);
        if (props.autoFocus) {
          transaction
            .getReactMountReady()
            .enqueue(AutoFocusUtils.focusDOMComponent, this);
        }
        break;
      case 'textarea':
        transaction.getReactMountReady().enqueue(textareaPostMount, this);
        if (props.autoFocus) {
          transaction
            .getReactMountReady()
            .enqueue(AutoFocusUtils.focusDOMComponent, this);
        }
        break;
      case 'select':
        if (props.autoFocus) {
          transaction