/**
 * Fire a warning if the custom element with the provided name isn't available.
 * @func defineElement
 * @param {HTMLElement} requester - Reference to the element requiring this custom element..
 * @param {string} elementName - Tag name of the required custom element.
 * @param {string} message - Optional message describing the consequences of it not begin available.
 */
export declare const demandCustomElement: (requester: HTMLElement, elementName: string, message?: string) => void;