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.

* TODO: Benchmark the effects of putting this at the top since 99% of props
   *       do not change for a given reconciliation.
   * TODO: Benchmark areas that can be improved with caching.
   *
   * @private
   * @param {object} lastProps
   * @param {object} nextProps
   * @param {?DOMElement} node
   */
  _updateDOMProperties: function(
    lastProps,
    nextProps,
    transaction,
    isCustomComponentTag,
  ) {
    var propKey;
    var styleName;
    var styleUpdates;
    for (propKey in lastProps) {
      if (
        nextProps.hasOwnProperty(propKey) ||
        !lastProps.hasOwnProperty(propKey) ||
        lastProps[propKey] == null
      ) {
        continue;
      }
      if (propKey === STYLE) {
        var lastStyle = lastProps[STYLE];
        for (styleName in lastStyle) {
          if (lastStyle.hasOwnProperty(styleName)) {