import type { SchemaValue } from '../schema.js';
import { type ValueConfig } from './value.js';
interface StringValueConfig<T extends string> extends ValueConfig<T> {
    emptyAllowed?: boolean;
    url?: boolean;
    regex?: RegExp;
    constrainTo?: readonly T[];
    ISODate?: boolean;
}
export declare class StringValue<T extends string = string> implements SchemaValue<string> {
    private value;
    private config;
    constructor(config?: StringValueConfig<T>);
    validate(value: T): string | null;
    get default(): T | undefined;
    get required(): boolean;
}
export declare function isString(value: unknown): value is string;
export {};