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.

* @see http://jsperf.com/obj-vs-arr-iteration
   *
   * @private
   * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
   * @param {object} props
   * @return {string} Markup of opening tag.
   */
  _createOpenTagMarkupAndPutListeners: function(transaction, props) {
    var ret = '<' + this._currentElement.type;
    for (var propKey in props) {
      if (!props.hasOwnProperty(propKey)) {
        continue;
      }
      var propValue = props[propKey];
      if (propValue == null) {
        continue;
      }
      if (registrationNameModules.hasOwnProperty(propKey)) {
        if (propValue) {
          ensureListeningTo(this, propKey, transaction);
        }
      } else {
        if (propKey === STYLE) {
          if (propValue) {
            if (__DEV__) {
              Object.freeze(propValue);
            }
          }
          propValue = CSSPropertyOperations.createMarkupForStyles(
            propValue,