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.

ret += ' ' + DOMPropertyOperations.createMarkupForID(this._domID);
    return ret;
  },
  /**
   * Creates markup for the content between the tags.
   *
   * @private
   * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
   * @param {object} props
   * @param {object} context
   * @return {string} Content markup.
   */
  _createContentMarkup: function(transaction, props, context) {
    var ret = '';
    
    var innerHTML = props.dangerouslySetInnerHTML;
    if (innerHTML != null) {
      if (innerHTML.__html != null) {
        ret = innerHTML.__html;
      }
    } else {
      var contentToUse = CONTENT_TYPES[typeof props.children]
        ? props.children
        : null;
      var childrenToUse = contentToUse != null ? null : props.children;
      if (contentToUse != null) {
        
        ret = escapeTextContentForBrowser(contentToUse);
        if (__DEV__) {
          setAndValidateContentChildDev.call(this, contentToUse);