Called when the element is moved into a new Document.
Invoke the Document#onEmbed callback when it is added to the DOM.
Called when the element is first removed from a Document. In cases where it is then moved into another Document, this callback is invoked before adoptedCallback, so we must also re-apply the prototype here so that subclasses have any disconnectedCallback overrides invoked appropriately.
A custom HTMLElement that is used to wrap enriched content that requires additional interactivity.