}
     *
     * Any properties used in the template that are not defined in _instanceProp
     * will be forwarded out to the Templatize `owner` automatically.
     *
     * Users may also implement the following abstract function to show or
     * hide any DOM generated using `stamp`:
     *
     *     _showHideChildren: function(shouldHide)
     *
     * Note that some callbacks are suffixed with `V2` in the Polymer 2.x behavior
     * as the implementations will need to differ from the callbacks required