export declare const $rule: {
    notExists: (key: string | 0, parent: string | null) => string;
    isNull: (name: string) => string;
    isBool: (name: string) => string;
    isLiteralOf: (name: string, literal: string) => string;
    isString: (name: string) => string;
    isNumber: (name: string) => string;
    isTimestamp: (name: string) => string;
    isServerTimestamp: (name: string) => string;
    isEmptyArray: (name: string) => string;
};