/**
 * Return the extension of the `path` with leading period.
 *
 * @example Usage
 * ```ts
 * import { extname } from "@std/path/windows/extname";
 * import { assertEquals } from "@std/assert";
 *
 * const ext = extname("file.ts");
 * assertEquals(ext, ".ts");
 * ```
 *
 * @param path The path to get the extension from.
 * @returns The extension of the `path`.
 */
export declare function extname(path: string): string;