A new mixin has been added: HTMLOrSVGElement
https://html.spec.whatwg.org/multipage/dom.html#htmlorsvgelement

interface mixin HTMLOrSVGElement {
  [SameObject] readonly attribute DOMStringMap dataset;
  attribute DOMString nonce;

  [CEReactions] attribute long tabIndex;
  void focus(optional FocusOptions options);
  void blur();
};
HTMLElement includes HTMLOrSVGElement;
SVGElement includes HTMLOrSVGElement;


We currently implement focus/blur/tabindex separately on HTMLElement and SVGElement. We currently implement nonce using NoncedElement.