/// <reference types="react" />
export type DRefExtra<T = HTMLElement> = (() => T | null) | string;
export declare function useRefExtra(refExtra?: string, update?: boolean): React.RefObject<HTMLElement>;
export declare function useRefExtra<T = HTMLElement>(refExtra?: () => T | null, update?: boolean): React.RefObject<T>;
export declare function useRefExtra<T = HTMLElement>(refExtra?: DRefExtra<T>, update?: boolean): React.RefObject<T | HTMLElement>;