The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

}
      } 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) {
      CSSPropertyOperations.setValueForStyles(
        getNode(this),
        styleUpdates,
        this
      );
    }
  },
  /**
   * Reconciles the children with the various properties that affect the
   * children content.
   *
   * @param {object} lastProps
   * @param {object} nextProps
   * @param {ReactReconcileTransaction} transaction