The popover="hint" global HTML attribute creates a popover that is subordinate to popovers with a popover="auto" attribute. You can use this to create tooltips that don't dismiss auto popovers.

The hidden="until-found" attribute hides an element until it is found using the browser's find-in-page search or it is directly navigated to by following a URL fragment.

Interest invokers, registered by the interestfor HTML attribute, trigger events and actions on a target element when a user shows interest in the element, through behaviors such as hover, focus, or long-press. Pseudo-elements apply styles to sources and targets of interest.

The blocking="render" attribute for <link>, <script>, and <style> elements blocks rendering until the external script or stylesheet has been loaded. For <link rel="expect">, rendering is blocked until a specific element is in the DOM.

The name="theme-color" attribute for the <meta> HTML element suggests a color that the browser can use to customize the display of the page or the browser user interface.

The headingoffset HTML attribute offsets the heading level of descendant <h1>–<h6> elements. The headingreset HTML attribute prevents heading offset computation from traversing beyond the element.

The focusgroup global HTML attribute combines descendant elements into a single tab stop, with arrow-key navigation between them, for toolbars, tabs, menus, radio groups, and other composite controls. It's an alternative to the sequential navigation of tabindex.