import { ZOptional } from '../optional/optional.mjs';
/**
 * Puts a . in front of name if one is not already there.
 *
 * If there are multiple dots in front of name, then
 * all dots but one is removed.
 *
 * @example
 *
 * ```ts
 * // Outputs .zip
 * castExtension('zip');
 *
 * // Outputs .zip
 * castExtension('.zip');
 *
 * // Outputs .zip
 * castExtension('...zip');
 * ```
 *
 * @param candidate -
 *        The candidate extension
 *
 * @returns
 *        The candidate prepended by a single dot.
 *        If candidate is undefined, null, the empty
 *        string, white space, or nothing but dots,
 *        then the empty string is returned.
 */
export declare function castExtension(candidate: ZOptional<string>): string;