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.

ensureListeningTo(this, propKey, transaction);
        }
      } else if (isCustomComponentTag) {
        if (!RESERVED_PROPS.hasOwnProperty(propKey)) {
          DOMPropertyOperations.setValueForAttribute(
            getNode(this),
            propKey,
            nextProp,
          );
        }
      } else if (
        DOMProperty.properties[propKey] ||
        DOMProperty.isCustomAttribute(propKey)
      ) {
        var node = getNode(this);
        
        
        
        if (nextProp != null) {
          DOMPropertyOperations.setValueForProperty(node, propKey, nextProp);
        } else {
          DOMPropertyOperations.deleteValueForProperty(node, propKey);
        }
      }
    }
    if (styleUpdates) {
      if (__DEV__) {
        ReactInstrumentation.debugTool.onHostOperation({
          instanceID: this._debugID,
          type: 'update styles',