Specs: registerElement(registerElement(...)) failed to work as expected

sky/examples/calculator/buttons.sky

 SKY MODULE - button widgets for calculator
 <!-- TODO(ianh): implement accessibility handling once the ax service exists -->
 
 <script>
   class AbstractButton extends Element {
     constructor (module) {
       super(module);
       let selector = new SelectorQuery('.dynamic');
       this.addEventListener('pointer-down', (event) => {
         selector.findAll(this.shadowRoot).every((element) => element.setAttribute('clicked'));
@@ skipping 37 matching lines @@
   div { background: green; color: yellow; }
   div[clicked] { background: yellow; color: green; }
  </style>
  <div class=dynamic>
   <content/>
  </div>
 </template>
 
 <script>
  module.exports = {
-   ThreeDButtonElement: module.registerElement({
-     tagName: 'graybutton',
-     shadow: true,
-     constructor: class extends AbstractButton {
+   ThreeDButtonElement: module.registerElement(
+     class extends AbstractButton {
+       static get tagName() { return 'graybutton'; }
+       static get shadow() { return true; }
        constructor (module) {
          super(module);
          this.shadowRoot.append(module.document.findId('threed-button-shadow-tree').cloneNode(true));
        }
-     },
-   }),
-   FlatButtonElement: module.registerElement({
-     tagName: 'graybutton',
-     shadow: true,
-     constructor: class extends AbstractButton {
+     }
+   ),
+   FlatButtonElement: module.registerElement(
+     class extends AbstractButton {
+       static get tagName() { return 'flatbutton'; }
+       static get shadow() { return true; }
        constructor (module) {
          super(module);
          this.shadowRoot.append(module.document.findId('flat-shadow-tree').cloneNode(true));
        }
-     },
-   }),
+     }
+   ),
  };
 </script>