import { Schema, MsgpackEncodingData, MsgpackRawStringProvider, JSONEncodingData, PrepareJSONOptions } from '../encoding.js';
/**
 * OptionalSchema allows for another schema-defined value to be optional.
 *
 * This expands the set of values which can be represented by the given schema to include `undefined`.
 *
 * Note that this schema considers `undefined` _and_ any default values from the underlying schema
 * to all be default values. This means that when using NamedMapSchema to omit default values, an
 * `undefined` value is indistinguishable from the given schema's default value; in this respect,
 * OptionalSchema does not affect the encoding of NamedMapSchema values, but rather allows the
 * application to restore omitted values as `undefined` instead of their default value.
 *
 * Upon decoding, this schema also allows null/undefined values to be acceptable as values.
 */
export declare class OptionalSchema extends Schema {
    readonly valueSchema: Schema;
    constructor(valueSchema: Schema);
    defaultValue(): undefined;
    isDefaultValue(data: unknown): boolean;
    prepareMsgpack(data: unknown): MsgpackEncodingData;
    fromPreparedMsgpack(encoded: MsgpackEncodingData, rawStringProvider: MsgpackRawStringProvider): unknown;
    prepareJSON(data: unknown, options: PrepareJSONOptions): JSONEncodingData;
    fromPreparedJSON(encoded: JSONEncodingData): unknown;
}