<!DOCTYPE html>
<script>
(function() {
    var proto = Object.create(HTMLElement.prototype);
    proto.createdCallback = function () {
        if (this.id == 'abortIt') {
            window.parent.checkLater();
            var e = window.frameElement
            e.parentNode.removeChild(e);
        }
    };

    var ctor = document.registerElement('x-a', {prototype: proto});
})();
</script>
<x-a></x-a>
<x-a></x-a>
<x-a id="abortIt"></x-a>
<x-a></x-a>
<x-a></x-a>