import { LitElement } from "lit";
import { Constructor } from "./Constructor";
/** A symbol through which to access the `ElementInternals` attached to an element. */
export declare const internals: unique symbol;
/** Defines functionality for an element attached to `ElementInternals`. */
export interface AttachInternalsMixin {
    /** The `ElementInternals` attached to the element. */
    readonly [internals]: ElementInternals;
}
/**
 * Determines whether a value is an `AttachInternalsMixin`.
 * @param {unknown} value The value to test.
 * @returns Whether `value` is an `AttachInternalsMixin`.
 */
export declare function isAttachInternalsMixin(value: unknown): value is AttachInternalsMixin;
/**
 * Mixin to augment an element with behavior that attaches to `ElementInternals`.
 * @template T The type of the base class.
 * @param {T} base The base class.
 * @param {boolean | undefined} formAssociated Whether the element is "Form Associated".
 * @returns {Constructor<AttachInternalsMixin> & T} A constructor that implements `AttachInternalsMixin`.
 */
export declare function AttachInternals<T extends Constructor<LitElement>>(base: T, formAssociated?: boolean): Constructor<AttachInternalsMixin> & T;
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