<element name="x-foo" constructor="XFoo">
<section>I'm an x-foo!</section>
<script>
  var section = this.querySelector('section');
  this.register({
    prototype: {
      readyCallback: function() {
        this.textContent = section.textContent; // this == <element>
      },
      foo: function() { alert('foo() called'); }
    }
  });
</script>
</element>