Javascript Prototype不显示输入

Question

我正在努力学习如何使用原型。我已经尝试了4种不同的方式来显示我的文本区域和按钮，但我无法弄清楚为什么它们不会出现。我已经评论了我尝试过的4个不同选项。有人请告诉我哪里可能出错了吗？

http://plnkr.co/edit/FSxbi5X1ri1gXJx5wkNw?p=preview

var PluralsightCommentProto = Object.create(HTMLElement.prototype);

PluralsightCommentProto.createdCallback = function() {
  this.innerHTML = "<h2>Pluralsight Comment</h2><textarea></textarea></br><input type='submit'>";
}

var PluralsightComment = document.registerElement('pluralsight-comment', {
  prototype: PluralsightCommentProto
});

//#Option 2
var comment = new PluralsightComment();
//document.body.appendChild(comment);

//Option 3
var comment = document.createElement('pluralsight-comment');
//document.body.appendChild(comment);

//Option 4
//document.body.innerHTML = '<pluralsight-comment />';

<pluralsight-comment></pluralsight-comment>