/**
 * Creates an async validator that checks username availability.
 *
 * @param checkFn - A function that returns a Promise resolving to `true` if available, else `false`.
 * @param message - Optional custom error message.
 */
declare const createUsernameAvailableValidator: (checkFn: (username: string) => Promise<boolean>, message?: string) => (username: string) => Promise<string | null>;
/**
 * Creates an async validator that validates email domain against a list of allowed domains.
 *
 * @param allowedDomains - List of allowed email domains (e.g., ["gmail.com"]).
 * @param message - Optional custom error message.
 */
declare const createEmailDomainValidator: (allowedDomains: string[], message?: string) => (email: string) => Promise<string | null>;

export { createEmailDomainValidator, createUsernameAvailableValidator };