Declarative Shadow DOM

Nice article on the shadow dom

We’re pleased to announce that support for the declarative shadow DOM API has been added and enabled by default in Safari Technology Preview 162. To recap, shadow DOM is a part of Web Components, a set of specifications that were initially proposed by Google to enable the creation of reusable widgets and components on the web. Since then these specifications have been integrated into the DOM and HTML standards. Shadow DOM, in particular, provides a lightweight encapsulation for DOM trees by allowing a creation of a parallel tree on an element called a “shadow tree” that replaces the rendering of the element without modifying its own DOM tree.