import validator from "validator";
import { Field } from "../field";
/** Validate.isString options. */
export interface IIsString extends validator.IsLengthOptions {
    /** Require lower case characters. */
    lowercase?: boolean;
    /** Require upper case characters. */
    uppercase?: boolean;
    /** Optional array of allowed values. */
    values?: string[];
}
/** Wrapper for validator methods isLength, isUppercase, isLowercase and isIn. */
export declare function isString(value?: string, options?: IIsString): string;
export declare class StringField extends Field<string> {
    protected readonly options: IIsString;
    constructor(options?: IIsString);
    validate(value: string): string;
}