@polymer/polymer/test/unit/dom-bind-elements2.html

The Polymer library makes it easy to create your own web components. Give your element some markup and properties, and then use it on a site. Polymer provides features like dynamic templates and data binding to reduce the amount of boilerplate you need to

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<script>
  Polymer({
    is: 'x-needs-host',
    attached: function() {
      if (!this.__dataHost) {
        throw "No dataHost at ready time";
      }
      this.config = this.__dataHost.getAttribute('config');
    }
  });
</script>