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 featuresThe 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.
Customized built-in elements are HTML elements that extend built-in elements using the is attribute, to add new behaviors that you define.