import { type HTMLTemplateResult, type ReactiveElement } from 'lit';
import { Controller } from '../Controller/index.js';
/**
 * A part of a component, extracted into a class of its own without introducing a component boundary.
 *
 * A part contributes a `template` to its host and may declare its own state, queries, events and
 * event listeners with the very same decorators a component uses. As a part shares the update
 * lifecycle of its host, changing its state re-renders the host as a whole - no properties have to
 * be passed down and no updates have to be propagated by hand.
 *
 * This makes a part the tool of choice to break up a large component, whereas a component should be
 * introduced whenever the extracted unit is reusable on its own.
 */
export declare abstract class ComponentPart<THost extends ReactiveElement = ReactiveElement> extends Controller {
    protected readonly host: THost;
    constructor(host: THost);
    /** The template of the part which its host renders. */
    get template(): HTMLTemplateResult;
    /**
     * Requests an update of the host.
     *
     * When a property key is provided, the change is tracked in the host's `changedProperties`
     * by a key unique to this part and property, so that it can neither collide with a property
     * of the host nor with one of another part.
     */
    requestUpdate(propertyKey?: PropertyKey, oldValue?: unknown): void;
}
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