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.

this,
          );
        }
        var markup = null;
        if (this._tag != null && isCustomComponent(this._tag, props)) {
          if (!RESERVED_PROPS.hasOwnProperty(propKey)) {
            markup = DOMPropertyOperations.createMarkupForCustomAttribute(
              propKey,
              propValue,
            );
          }
        } else {
          markup = DOMPropertyOperations.createMarkupForProperty(
            propKey,
            propValue,
          );
        }
        if (markup) {
          ret += ' ' + markup;
        }
      }
    }
    
    
    if (transaction.renderToStaticMarkup) {
      return ret;
    }
    if (!this._hostParent) {
      ret += ' ' + DOMPropertyOperations.createMarkupForRoot();
    }