import { LitElement } from 'lit';
/**
 * Requests an animation frame and waits for it to be resolved.
 *
 * @param callback - Invoked on the next animation frame.
 */
export declare function raf(callback?: () => void): Promise<number>;
/**
 * Builds an `exportsparts` attribute value given an array of `parts` and an optional `prefix`.
 *
 * @param parts
 * @param prefix
 */
export declare function buildExportPartsAttr(parts: string[], prefix: string | ((part: string) => string)): string;
/**
 * Registers a custom element in the CustomElementRegistry. By "safely" we mean:
 *
 * - Called only client-side (`window` is defined).
 * - The element is only registered if it hasn't been registered before under the given `name`.
 *
 * @param name - A string representing the name you are giving the element.
 * @param constructor - A class object that defines the behaviour of the element.
 * @param isClient
 */
export declare function safelyDefineCustomElement(name: string, constructor: CustomElementConstructor, isClient?: boolean): void;
/**
 * Sets an attribute on the given `el`. If the `attrValue` is `undefined`or `null` the attribute
 * will be removed.
 *
 * @param element - The element to set the attribute on.
 * @param attrName - The name of the attribute.
 * @param attrValue - The value of the attribute.
 */
export declare function setAttribute(element: Element, attrName: string, attrValue?: string | boolean | undefined | null): void;
/**
 * Returns elements assigned to the given slot in the shadow root. Filters out all nodes
 * which are not of type `Node.ELEMENT_NODE`.
 *
 * @param el - The element containing the slot.
 * @param name - The name of the slot (optional).
 */
export declare function getSlottedChildren(el: HTMLElement, name?: string): Element[];
export declare function getElementAttributes(elementCtor: typeof LitElement): Set<string>;
export declare function observeAttributes(element: Element, attributes: Set<string>, onChange: (attrName: string, attrValue: string | null) => void): MutationObserver;