/**
 * Finds exactly one element matching the selector. When the selector starts
 * with `#`, both `id` and `name` attributes are tried.
 *
 * @example
 *     const input = selectOne<HTMLInputElement>('#email');
 *     const btn = selectOne<HTMLButtonElement>('.submit', form);
 */
export declare function selectOne<T extends Element = HTMLElement>(selector: string, parent?: Element | Document): T;
/**
 * Sets a validation error on a form field found by selector. Supports native
 * form elements and form-associated custom elements using `ElementInternals`.
 *
 * @example
 *     formError('#email', 'Please enter a valid email');
 *     formError('#email', ''); // clears the error
 */
export declare function formError(selector: string, message: string, parent?: Element | Document): void;