2024
1 featuresThe :state() CSS pseudo-class matches custom elements based on their custom state, set through the ElementInternals.states API.
2023
1 featuresCustom elements may act like built-in form elements, via the attachInternals() method of HTMLElement and the ElementInternals API.
2020
1 featuresAutonomous custom elements are HTML elements with a hyphenated tag name (like <example-element>) that have behaviors you define.
Limited Availability
2 featuresCustomized built-in elements are HTML elements that extend built-in elements using the is attribute, to add new behaviors that you define.
The CustomElementRegistry() constructor creates a new custom element registry that's separate from the global window.customElements registry. Creating more than one registry is useful for multiple custom elements that have the same tag name to coexist.