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.

var lastChildren = lastContent != null ? null : lastProps.children;
    var nextChildren = nextContent != null ? null : nextProps.children;
    
    
    var lastHasContentOrHtml = lastContent != null || lastHtml != null;
    var nextHasContentOrHtml = nextContent != null || nextHtml != null;
    if (lastChildren != null && nextChildren == null) {
      this.updateChildren(null, transaction, context);
    } else if (lastHasContentOrHtml && !nextHasContentOrHtml) {
      this.updateTextContent('');
      if (__DEV__) {
        ReactInstrumentation.debugTool.onSetChildren(this._debugID, []);
      }
    }
    if (nextContent != null) {
      if (lastContent !== nextContent) {
        this.updateTextContent('' + nextContent);
        if (__DEV__) {
          setAndValidateContentChildDev.call(this, nextContent);
        }
      }
    } else if (nextHtml != null) {
      if (lastHtml !== nextHtml) {
        this.updateMarkup('' + nextHtml);
      }
      if (__DEV__) {
        ReactInstrumentation.debugTool.onSetChildren(this._debugID, []);
      }
    } else if (nextChildren != null) {