/**
 * Context Protocol
 * @link https://github.com/webcomponents-cg/community-protocols/blob/main/proposals/context.md
 */
/**
 * A context key.
 *
 * A context key can be any type of object, including strings and symbols. The
 *  Context type brands the key type with the `__context__` property that
 * carries the type of the value the context references.
 */
export type Context<KeyType, ValueType> = KeyType & {
    __context__: ValueType;
};
/**
 * An unknown context type
 */
export type UnknownContext = Context<unknown, unknown>;
/**
 * A helper type which can extract a Context value type from a Context type
 */
export type ContextType<T extends UnknownContext> = T extends Context<infer _, infer V> ? V : never;
/**
 * A function which creates a Context value object
 */
export declare function createContext<ValueType>(key: unknown): Readonly<Context<typeof key, ValueType>>;
/**
 * A callback which is provided by a context requester and is called with the value satisfying the request.
 * This callback can be called multiple times by context providers as the requested value is changed.
 */
export type ContextCallback<ValueType> = (value: ValueType, unsubscribe?: () => void) => void;
/**
 * An event fired by a context requester to signal it desires a named context.
 *
 * A provider should inspect the `context` property of the event to determine if it has a value that can
 * satisfy the request, calling the `callback` with the requested value if so.
 *
 * If the requested context event contains a truthy `subscribe` value, then a provider can call the callback
 * multiple times if the value is changed, if this is the case the provider should pass an `unsubscribe`
 * function to the callback which requesters can invoke to indicate they no longer wish to receive these updates.
 */
export declare class ContextRequestEvent<T extends UnknownContext> extends Event {
    readonly context: T;
    readonly callback: ContextCallback<ContextType<T>>;
    readonly subscribe?: boolean | undefined;
    constructor(context: T, callback: ContextCallback<ContextType<T>>, subscribe?: boolean | undefined);
}
declare global {
    interface HTMLElementEventMap {
        /**
         * A 'context-request' event can be emitted by any element which desires
         * a context value to be injected by an external provider.
         */
        'context-request': ContextRequestEvent<Context<unknown, unknown>>;
    }
}