Form-associated custom elementsCustom elements may act like built-in form elements, via the attachInternals() method of HTMLElement and the ElementInternals API.custom-elementsCustom elementswidely2023-03-272025-09-27https://html.spec.whatwg.org/multipage/custom-elements.html#form-associated-custom-elementshttps://developer.mozilla.org/docs/Web/API/ElementInternalsapi.ElementInternalsapi.ElementInternals.checkValidityapi.ElementInternals.formapi.ElementInternals.labelsapi.ElementInternals.reportValidityapi.ElementInternals.setFormValueapi.ElementInternals.setValidityapi.ElementInternals.validationMessageapi.ElementInternals.validityapi.ElementInternals.willValidateapi.HTMLElement.attachInternalshttps://nowyoucanuse.com/features--form-associated-custom-elements.html