export interface ExtendableLike {
    extensions?: Record<string, unknown> | null | undefined;
}
export declare function getExtensions(extendable: ExtendableLike): Record<string, unknown>;
export declare function hasExtension(extendable: ExtendableLike, key: string | symbol): boolean;
export declare function getExtension<T = unknown>(extendable: ExtendableLike, key: string | symbol): T | undefined;
export declare function getExtension<T = unknown>(extendable: ExtendableLike, key: string | symbol, fallback: T): T;
export declare function setExtension(extendable: ExtendableLike, key: string | symbol, value: unknown): void;