export declare class UnicodeString {
    value: string;
    private _chars;
    constructor(value: string);
    private get chars();
    get size(): number;
    get isEmpty(): boolean;
    charAt(index: number): string;
    substring(start: number, end?: number): UnicodeString;
    [Symbol.toPrimitive](hint: any): string | number;
    toString(): string;
    valueOf(): string;
}